Roast Salmon With Leeks and Onions

The smell of caramelized leeks in a hot oven always reminds me of weeknights when I needed something impressive but couldn't face another pan to scrub. I'd started sliding salmon onto sheet pans with whatever vegetables looked good, and one evening I tossed in leeks with red onion and lemon slices. The salmon came out perfectly moist, the vegetables sweet and tender, and I realized I'd been overcomplicating dinner for years. That bright parsley dressing came later, after a friend mentioned her grandmother always finished fish with something green and sharp.

I made this for my sister when she came over stressed and hungry after a long day. She sat at the counter while I chopped parsley, and we talked about nothing important while the oven did all the work. When I plated it and spooned that green dressing over the top, she looked at me like I'd performed magic. It wasn't magic, just good timing and a handful of ingredients that knew how to behave together.

Ingredients

• Salmon fillets, skin-on: The skin protects the delicate flesh from drying out and crisps up nicely if you sear it later, though in the oven it stays tender.
• Leeks: Slice them into thick rounds so they hold their shape and turn sweet without falling apart; always rinse well between the layers to remove grit.
• Red onion: Cut into wedges and they roast into soft, sweet ribbons that balance the richness of the fish.
• Olive oil: Use enough to coat the vegetables so they caramelize instead of steaming.
• Lemon slices: They look pretty and their juice seeps into the salmon as it cooks, adding brightness without any effort.
• Fresh flat-leaf parsley: The backbone of the dressing; curly parsley works but flat-leaf has a cleaner, more vibrant flavor.
• Garlic clove: Minced finely so it blends into the dressing without overpowering the parsley.
• Dijon mustard: Adds a subtle tang and helps emulsify the dressing so it clings to the salmon.
• Capers: Salty, briny little bursts that wake up the whole dish; chop them so they distribute evenly.
• Lemon zest and juice: The zest carries essential oils that make the dressing smell incredible, and the juice keeps it bright and balanced.

Instructions

Preheat and Prep:

Set your oven to 400°F so it's fully heated when the vegetables go in. Gather your leeks, onion, and salmon while it warms.

Start the Vegetables:

Spread the leeks and red onion on a large baking sheet, drizzle with olive oil, season with salt and pepper, and toss with your hands to coat everything evenly. Roast them for 10 minutes until they start to soften and the edges turn golden.

Add the Salmon:

Pull the pan from the oven and nestle the salmon fillets skin-side down among the vegetables, then lay lemon slices over the top. Slide it back in and roast for 12 to 15 minutes, until the salmon flakes easily and the vegetables are tender.

Make the Dressing:

While the salmon cooks, combine parsley, garlic, Dijon, capers, lemon zest, olive oil, and lemon juice in a small bowl. Stir until it comes together, then taste and adjust with salt and pepper.

Serve:

Transfer the salmon and vegetables to plates, spoon the parsley dressing generously over each fillet, and serve right away while everything is warm and fragrant.

Save

The first time I served this to guests, someone asked if I'd taken a cooking class. I laughed and said no, just a willingness to let the oven do the heavy lifting. That parsley dressing, vibrant and sharp, made the whole plate look like I'd put in twice the effort. It became my quiet secret for looking like a better cook than I probably am.

What to Serve Alongside

I usually keep it simple with roasted baby potatoes tossed in the same olive oil or a bowl of steamed jasmine rice to soak up the dressing. A crisp green salad with a light vinaigrette works if you want more vegetables, or crusty bread if you're in the mood to mop up every last bit of that garlicky parsley oil.

Swaps and Variations

Trout fillets work beautifully if you prefer a milder fish, and thick cod steaks hold up well too, though they may need an extra minute or two in the oven. If leeks are hard to find, use two fennel bulbs sliced into wedges for a subtle anise sweetness. You can add a pinch of crushed red pepper flakes to the dressing if you like a little heat threading through the brightness.

Storage and Reheating

Leftovers keep in the fridge for up to two days in an airtight container, though the salmon tastes best eaten cold or at room temperature rather than reheated. The parsley dressing stays fresh for three days and makes a great drizzle over grilled chicken or roasted carrots. If you do reheat, use a low oven (300°F) and cover the fish loosely with foil so it doesn't dry out.

• Store the dressing separately so it stays vibrant and doesn't make the fish soggy.
• Flake leftover salmon over salad greens with the dressing for an easy next-day lunch.
• Freeze extra salmon fillets before cooking, but don't freeze the finished dish as the texture suffers.

Save

This dish has become my answer to the question of what to cook when I want something nourishing without spending an hour at the stove. The parsley dressing makes it feel special, and the one-pan approach keeps it real.

Recipe FAQs

→ Can I use frozen salmon fillets?

Yes, you can use frozen salmon fillets. Make sure to thaw them completely in the refrigerator overnight and pat them dry before roasting to ensure proper cooking and browning.

→ What can I substitute for leeks?

If leeks aren't available, you can substitute with sliced fennel bulb, spring onions, or additional red onions. Each will provide a slightly different flavor profile but will work well with the salmon.

→ How do I know when the salmon is cooked through?

The salmon is done when it flakes easily with a fork and reaches an internal temperature of 145°F (63°C). The flesh should be opaque and slightly pink in the center for optimal texture.

→ Can I make the parsley dressing ahead of time?

Absolutely. The dressing can be prepared up to 2 days in advance and stored in an airtight container in the refrigerator. Stir well before serving as the ingredients may separate.

→ What sides pair well with this dish?

This salmon pairs beautifully with roasted potatoes, steamed rice, quinoa, or crusty bread. A simple green salad or roasted asparagus also complements the flavors nicely.

→ Can I use a different type of fish?

Yes, this preparation works well with trout, cod, halibut, or sea bass. Adjust cooking time based on the thickness of the fillets, checking for doneness a few minutes earlier for thinner cuts.