Baked Cod with Potatoes and Onions Recipe: One-Pan Herb-Roasted Harmony

This baked cod with potatoes and onions recipe delivers a foolproof, restaurant-quality meal with minimal effort—just one pan, simple ingredients, and 30 minutes of active time.

The secret lies in roasting everything together, where the cod stays moist while the potatoes develop crispy edges and the onions caramelize into sweet, golden perfection.

I perfected this method after years of testing, ensuring the fish never dries out and the vegetables achieve that ideal balance of texture and flavor.

The beauty of this dish is its simplicity: no fancy techniques, no special equipment, just a one-pan approach that transforms fresh ingredients into a hearty, satisfying meal. The potatoes and onions roast in their own juices, absorbing the aromatic herbs and garlic-infused butter, while the cod bakes gently atop them.

This method not only saves time but also ensures every bite is packed with flavor—no soggy fish or bland vegetables here.

By the time it comes out of the oven, you’ll have tender, flaky cod with a delicate seasoning, paired with crispy, golden potatoes and caramelized onions that add depth to every bite.

The dish is elegant enough for a weeknight dinner but hearty enough to feed a family—no fuss, no stress, just a meal that feels like a hug. The aroma alone will have everyone at the table asking what’s for dinner.

Serve it with a squeeze of lemon and a sprinkle of fresh parsley for a touch of brightness, or pair it with a simple green salad to round out the meal.

This recipe is designed to work with whatever you have on hand, making it perfect for both casual dinners and special occasions. Let’s get started—your one-pan masterpiece is just minutes away.

Ingredients for baked cod with potatoes and onions

Twelve simple ingredients transform into a restaurant-worthy one-pan meal.

The cod is the star, so prioritize quality here. Look for center-cut fillets at your local fishmonger—they stay moist longer. If buying frozen, thaw overnight in the fridge (never in warm water). For the potatoes, baby Yukon Golds from Whole Foods or Trader Joe's develop the best caramelized edges. Onions should be firm with no soft spots—yellow or red varieties work equally well. Fresh herbs make all the difference: Penzeys or your grocery store's bulk section are great for rosemary and thyme. The butter should be cold when you cube it—Land O'Lakes or Plugrá are reliable choices, but any unsalted brand works.

No fresh herbs? Dried rosemary and thyme at one-third the amount will work, but the flavor won't be as bright. Substituting cod? Haddock or halibut work equally well—just adjust baking time by 2-3 minutes. For the potatoes, red potatoes hold their shape better if you prefer softer texture. The lemon zest can be swapped for 1 tsp bottled zest, but fresh is always better. If you're short on time, pre-minced garlic from the jar is fine (just check the ingredients list—no additives). The olive oil can be omitted entirely if you're watching calories, but it helps the vegetables roast more evenly.

This dish reheats beautifully—just cover with foil and warm in a 350°F oven for 10 minutes. Store leftovers in an airtight container for up to 3 days, though I find the flavor peaks on day two. For meal prep, portion the potatoes and onions separately—they reheat better alone. The cod is best eaten fresh, but you can reheat it gently if needed. Freezing isn't recommended for this dish, as the cod tends to dry out. To save time, parboil the potatoes for 5 minutes before roasting—they'll cook more evenly and develop crispier edges.

Step-by-step instructions for baked cod with potatoes and onions

This one-pan method delivers perfectly flaky cod with crispy potatoes and caramelized onions every time.

Preheat your oven to 400°F while you prepare the vegetables. Cut the 1.5 lb baby potatoes in half, leaving the skin on for texture. Quarter the 1 whole yellow onion, keeping the skin on for deeper flavor as it caramelizes. Toss both in a large bowl with 1 tablespoon of the extra-virgin olive oil, 1 teaspoon of the sea salt, and 0.25 teaspoon of the freshly ground black pepper.

Pat the 2 whole cod fillets dry with paper towels—this ensures crispy skin. Place them on a separate plate and season generously with the remaining 0.5 teaspoon sea salt and 0.25 teaspoon black pepper. Sprinkle evenly with the 1 tablespoon lemon zest and 1 tablespoon fresh thyme leaves. The zest adds a bright citrus note that balances the richness of the cod.

In a large, oven-safe skillet with a lid, melt 2 tablespoons of the unsalted butter over medium heat. Add the minced 4 cloves garlic and cook for 30 seconds until fragrant—don't let it brown or it'll turn bitter. Remove the pan from heat and stir in the 2 tablespoons chopped fresh rosemary.

Arrange the seasoned cod fillets in the skillet, skin-side down if present. Scatter the prepared potatoes and onions around the cod, creating a single layer. Dot the top with the remaining 2 tablespoons unsalted butter, cutting it into small cubes first so it melts evenly. The butter bastes the fish and vegetables as they bake, creating a golden crust.

Transfer the skillet to the preheated oven and bake uncovered for 20 minutes. After this initial bake, the potatoes should begin to soften and the onions should start caramelizing. Carefully flip the cod fillets using a fish spatula—be gentle to avoid breaking the delicate flesh—and sprinkle with the remaining 1 tablespoon chopped fresh rosemary.

Continue baking for another 12-15 minutes until the cod flakes easily when tested with a fork and the potatoes are tender with crisp edges. The onions should be deep golden brown and caramelized. If the top isn't browning enough, broil for 2-3 minutes at the end, watching closely to prevent burning.

Remove the skillet from the oven and let it rest for 5 minutes before serving. This resting period allows the juices to redistribute in the cod, ensuring maximum tenderness. Drizzle the baked dish with the 2 tablespoons lemon juice and toss gently to combine. The acidity brightens the flavors and cuts through the richness of the butter and fish.

Garnish with the 0.25 cup chopped fresh parsley just before serving. The parsley adds a fresh contrast to the herbaceous notes from the rosemary and thyme. Serve immediately with the pan juices spooned over the top—every bite should deliver flaky cod, crispy potatoes, and sweet caramelized onions in perfect harmony.

Troubleshooting your baked cod with potatoes and onions

Cod Too Dry?

If your cod ends up dry, you likely overcooked it or didn’t season it properly before baking. First, always use center-cut cod fillets—they stay moist longer. Pat them very dry with paper towels before seasoning, as moisture on the surface steams the fish instead of browning it.

Bake at 400°F for no more than 15 minutes total—overcooking is the #1 cause of dryness. For extra insurance, add a thin slice of lemon under each fillet while baking. 🍋

Potatoes Still Hard?

Undercooked potatoes usually mean they weren’t cut evenly or didn’t have enough time to tenderize. Halve them uniformly (about ½-inch thick) so they cook at the same rate. For extra crispiness, parboil them for 5 minutes before roasting—they’ll develop a better crust.

If they’re still firm after baking, return them to the oven for 5-10 more minutes at 400°F, covered with foil to trap steam. A meat thermometer should read 205-210°F for perfect doneness.

Onions Not Caramelized?

Onions need time to break down and develop sweetness. Quarter them skin-on and spread them out in a single layer—they’ll caramelize more evenly. For deeper flavor, sauté them for 2-3 minutes in the skillet before adding the cod and potatoes.

If they’re still pale after baking, broil for 2-3 minutes at the end, watching closely to avoid burning. A splash of 1 teaspoon balsamic vinegar before baking can also help speed up caramelization. 🧅

Fish Stuck to Pan?

This happens when the cod isn’t properly prepped or the pan isn’t hot enough. Always pat the cod completely dry before seasoning—moisture causes sticking. Heat your skillet over medium heat for 1 minute before adding the butter and garlic to create a nonstick surface.

If it still sticks, gently slide a fish spatula under the fillets at a 45-degree angle—never force it. A light coating of olive oil on the pan before buttering can also help prevent sticking.

Uneven Cooking?

If the edges cook faster than the center, your pan is likely too crowded. Arrange the potatoes and onions in a single layer with the cod fillets spaced ½-inch apart. Avoid overfilling the pan—use a 12-inch oven-safe skillet for this recipe.

For even browning, rotate the pan halfway through baking (after 10 minutes). If your oven runs hot, reduce the temperature to 375°F to prevent overcooking the outer edges while the center stays underdone.

Flavor Too Mild?

This usually means the herbs or seasoning weren’t distributed properly. Toss the potatoes and onions generously with salt and pepper before baking, and sprinkle fresh herbs directly on top of the cod and vegetables.

For extra depth, add 1 teaspoon smoked paprika to the butter or 1 minced shallot with the garlic. A final squeeze of lemon juice and a sprinkle of flaky sea salt right before serving can also elevate the flavors dramatically. 💫

Frequently asked questions