Side Dishes
This baked cod with potatoes and onions recipe delivers a complete, restaurant-quality meal straight from your oven with minimal effort. The secret lies in layering flavors through a simple yet precise method that transforms humble ingredients into a harmonious, one-pan dish.
I've perfected this technique after years of testing, ensuring the cod remains tender while the potatoes achieve a crispy exterior and fluffy interior.
The beauty of this recipe is its simplicity—just three core ingredients, a few pantry staples, and a single baking sheet. The cod fillets are seasoned with herbs and lemon, while the potatoes and onions are tossed in olive oil, garlic, and thyme, creating layers of aromatic flavor.
Baking everything together allows the ingredients to meld naturally, resulting in a dish that's both comforting and elegant.
By the time it emerges from the oven, you'll have golden, crispy potatoes and onions surrounding perfectly cooked cod with a delicate, flaky texture.
The aroma alone will have everyone gathering around the table, and the first bite delivers a balance of savory, herby, and slightly tangy flavors that make this dish feel like a special occasion. The best part?
It requires less than 45 minutes of active time and only one pan to clean.
Serve this dish with a simple green salad or steamed vegetables for a complete meal that's perfect for weeknight dinners or weekend gatherings. The recipe scales easily, so you can adjust the portions to feed a crowd or just two. Let's create this flavorful, cohesive meal together.
Ingredients for baked cod with potatoes and onions
Three core ingredients, one pan, restaurant-quality harmony in every bite.
| Ingredient | Amount | Notes |
|---|---|---|
| Cod Fillets 🐟 | 4 whole | Skin-on for crispiness, 6-8 oz each |
| Russet Potatoes 🥔 | 2 lbs | Waxy variety preferred, cut into 1-inch cubes |
| Yellow Onions 🧅 | 2 whole | Medium size, sliced into 1/4-inch rings |
| Extra-Virgin Olive Oil 🫒 | ⅓ cup | Light fruity variety for balance |
| Fresh Thyme Leaves 🌿 | ¼ cup | Stems removed, finely chopped |
| Garlic Cloves 🧄 | 6 cloves | Minced, not pre-minced jarred |
| Lemon Juice 🍋 | ¼ cup | Freshly squeezed, no pulp |
| Salt 🧂 | 1 ½ tbsp | Diamond Crystal preferred |
| Ground Black Pepper 🌶️ | 1 tsp | Freshly cracked preferred |
| Fresh Dill 🌿 | ⅛ cup | Chopped, for cod seasoning |
| Fresh Parsley 🌿 | ⅛ cup | Chopped, for garnish |
| Fresh Lemon Zest 🍋 | 1 tbsp | From 1/2 lemon, for brightness |
The cod selection is critical—look for skin-on fillets with even thickness, typically 6-8 ounces each. Whole Foods and Trader Joe's carry excellent options, but any seafood counter will work. If buying frozen, thaw overnight in the fridge—never under running water. The potatoes should be russet or Yukon Gold for their fluffy texture when baked. For the onions, yellow or red varieties add subtle sweetness, but white works too. Fresh herbs are non-negotiable here—they make all the difference between good and exceptional flavor.
No fresh thyme? Dried thyme at one-third the amount will suffice, though the flavor won't be identical. Short on dill? Fresh parsley at double the quantity provides a milder but acceptable alternative. The olive oil should be extra-virgin—less expensive varieties can taste bitter. For lemon juice, freshly squeezed is essential—bottled juice lacks the bright acidity needed to balance the dish. If you're preparing ahead, you can chop all vegetables and store them separately in the fridge for up to 24 hours before baking. The cod should be seasoned just before baking to maintain its delicate texture.
This dish reheats beautifully—simply cover with foil and warm in a 350°F oven for 10-15 minutes. For storage, keep components separate: refrigerate the cod and vegetables in airtight containers for up to 3 days. The baked potatoes and onions can be prepped ahead and stored for 2 days before adding the cod. When freezing, wrap the cod tightly in plastic wrap and foil, then freeze for up to 3 months. Thaw completely in the fridge before reheating. The lemon zest and juice can be prepped 1 day ahead and stored in an airtight container in the fridge.
Why You'll Love This Recipe
- One-Pan Magic: I swear by this trick—just toss everything on a sheet pan, drizzle with olive oil, and let the oven work its magic. No pots, no pans, no stress.
- Thyme for Success: That fresh thyme? It’s the secret weapon here. The bright, earthy aroma clings to the crispy cod and caramelized onions like a hug from your favorite chef.
- Leftovers That Win: Honestly, I always make extra because the flavors get even better the next day. Reheat those potatoes until golden, and the cod flakes apart like a dream—no sad, dry leftovers here.
- Budget-Friendly Feast: Cod fillets and russets are affordable, and onions stretch every bite. It’s the kind of meal where you feed a crowd without breaking the bank—or your grocery budget.
Step-by-step instructions for baked cod with potatoes and onions
This one-pan method delivers perfectly crisp cod, tender potatoes, and caramelized onions with minimal effort.
Prep and Season the Cod and Vegetables
Preheat your oven to 400°F. Pat the 4 whole cod fillets dry with paper towels—this ensures crispy skin later. Place them skin-side down on a parchment-lined baking sheet. Season each fillet generously with 1.5 tablespoons salt and 1 teaspoon ground black pepper, dividing the amounts evenly.
Next, cut the 2 lbs russet potatoes into 1-inch cubes and toss them in a large bowl with 0.33 cup extra-virgin olive oil. Spread the potatoes evenly around the cod fillets, leaving space between pieces for even cooking. Peel and slice the 2 whole yellow onions into ¼-inch rings, then arrange them in a ring around the potatoes, slightly overlapping. This creates a beautiful presentation while allowing flavors to meld.
Create the Herb and Garlic Mixture
In a small bowl, combine the 0.25 cup fresh thyme leaves, 6 cloves minced garlic, 0.25 cup lemon juice, and 1 tablespoon fresh lemon zest. Mix well to create a bright, aromatic paste. Spoon this mixture evenly over the potatoes and onions, ensuring every surface gets coated. This step infuses the vegetables with deep flavor while balancing the richness of the cod.
Don't skip this step—it's what transforms simple vegetables into something extraordinary. The thyme and garlic will mellow slightly during baking, but their bright, herbal notes will shine through.
Bake Until Golden and Tender
Transfer the baking sheet to the preheated oven and bake for 25 minutes. After this initial baking time, carefully flip the cod fillets using a spatula—this prevents them from breaking apart. Return the sheet to the oven and continue baking for another 15-20 minutes, or until the cod flakes easily with a fork and the potatoes are fork-tender with slightly crisp edges.
You'll know the potatoes are done when they yield to gentle pressure and develop a golden-brown crust. The onions should be soft and caramelized, with their edges slightly browned. The cod should be opaque throughout with no translucent centers.
Finish with Fresh Herbs and Rest
Remove the baking sheet from the oven and let everything rest for 5 minutes. This resting period allows the juices to redistribute, ensuring each bite of cod remains moist. While resting, sprinkle the 0.125 cup fresh dill and 0.125 cup fresh parsley evenly over the top. The herbs add a final burst of freshness that contrasts beautifully with the rich, baked flavors.
Serve immediately, dividing the potatoes and onions evenly among plates. The cod should be presented whole or flaked over the vegetables, allowing diners to enjoy the full flavor harmony. Pair with a simple green salad or crusty bread to complete the meal.
Pro Tips For Making Baked Cod With Potatoes And Onions
- Parboil Potatoes First: Cut the potatoes into even 1-inch chunks, then boil them for 5 minutes before roasting—this guarantees they’ll crisp up instead of turning mushy. I learned this the hard way when my first batch emerged as sad, limp potatoes instead of golden, fluffy clouds.
- Salt the Cod Generously: Season the cod fillets with salt right after patting them dry—don’t wait until the last minute. The salt needs time to draw out moisture so the skin crisps properly. (Yes, even if you’re impatient like me.)
- Sear Onions Before Mixing: Caramelize the sliced onions in olive oil for 8–10 minutes until soft and golden before tossing them with the potatoes. This adds depth of flavor that raw onions just can’t match—my grandmother swore by this, and she was right.
- Use a Meat Thermometer: Pull the cod out of the oven when it hits 145°F (63°C)—any higher, and it’ll turn rubbery. The internal temp is more reliable than guessing by appearance, especially if your oven runs hot or cold. (Your future self will thank you.)
Storing and reheating your baked cod with potatoes and onions
Refrigerator Storage
Store the baked cod and vegetables separately in airtight containers to maintain freshness. Place the cod in a shallow dish with a sprinkle of lemon juice and 1 tablespoon olive oil to prevent drying. The potatoes and onions can share a container but should be kept dry.
Refrigerate for up to 3 days—the cod stays tender, while the vegetables hold their texture. For best results, reheat the cod and vegetables together in the oven. 🌡️
Freezer Prep
Wrap each cod fillet tightly in plastic wrap, then place in a freezer-safe bag with lemon zest and 1 tablespoon olive oil to preserve moisture. Freeze for up to 3 months.
For the potatoes and onions, toss them in 1 tablespoon olive oil and store in a single airtight container for up to 2 months. Thaw cod overnight in the fridge before reheating. Never refreeze thawed cod. ❄️
Oven Reheating
For the best texture, cover the entire baking sheet with aluminum foil and reheat at 350°F for 10-15 minutes. This gentle method prevents the cod from drying out while restoring the potatoes' crisp edges.
Add a splash of water or broth if the vegetables seem dry. The cod should reach an internal temperature of 145°F for safe reheating. 🔥
Microwave Shortcut
If you're short on time, transfer the cod and vegetables to a microwave-safe dish, cover loosely with a damp paper towel, and heat on 50% power for 2-3 minutes. Stir halfway through to redistribute heat.
This method works best for the potatoes and onions but may slightly dry out the cod. Always check the internal temperature to ensure it reaches 145°F. ⚡
Garnish Before Serving
After reheating, brighten the dish with fresh parsley or dill, a squeeze of lemon juice, and a drizzle of olive oil. These finishing touches restore the vibrant flavors lost during storage.
Serve immediately to enjoy the crispness and freshness of the vegetables. The cod will taste as if it was just baked. 💫
Meal Prep Tips
Prep the potatoes and onions 1 day ahead and store them in the fridge. Season the cod just before baking to keep it tender. For a quick weeknight meal, assemble everything on a baking sheet and reheat straight from the fridge.
This strategy cuts active cooking time to just 20 minutes while keeping the dish restaurant-quality. 📅
Nutrition facts
Frequently asked questions
Can I use frozen cod instead of fresh?
Yes, but thaw it properly first. Place frozen cod fillets in a sealed bag and refrigerate overnight (about 12-24 hours) for even thawing. Never microwave-thaw as it can make the meat unevenly cooked. Pat them completely dry before seasoning to ensure crispy skin. The baking time remains the same as for fresh cod.
What's the best way to keep the cod from sticking to the pan?
Use parchment paper or a silicone baking mat to create a non-stick barrier. If you prefer direct baking, pat the cod fillets very dry with paper towels before seasoning—moisture is the enemy of crispy skin. Also, arrange the potatoes and onions around the cod rather than directly under them to prevent steam buildup.
Can I make this dish in a foil packet?
Line a large sheet of heavy-duty foil with parchment paper, then arrange the cod, potatoes, and onions in the center. Drizzle with olive oil, lemon juice, and herbs, then fold the foil tightly to seal. Bake at 400°F for 30-35 minutes until the potatoes are tender. This method creates a steamy environment that keeps everything moist while concentrating flavors.
How do I adjust the recipe for a larger group?
Double or triple the ingredients while using a larger baking sheet. For 8 servings, use 8 cod fillets, 4 lbs potatoes, and 4 onions. Increase oven capacity by using two baking sheets simultaneously. Bake times remain similar, but check for doneness at the lower end of the range since larger portions may cook slightly faster.
What if my cod is overcooked?
Overcooked cod becomes dry and flaky. If this happens, try flaking the fish gently and mixing it with a sauce like lemon butter or beurre blanc to restore moisture. For future attempts, reduce the baking temperature to 375°F and check doneness at 10 minutes before the estimated time. Use a meat thermometer to confirm 145°F internal temperature.