Roasted Mahi Mahi with Caramelized Onions and Lemon Butter
Prep
15 mins
Cook
35 mins
Servings
4
Difficulty
Easy
This is one of my favorite weeknight dinners because it comes together in just 50 minutes total, yet tastes like something from a fancy restaurant. Mahi mahi is such a wonderful fish to work with, mild and flaky, and it's packed with lean protein and omega 3 fatty acids that are great for your heart. The magic happens when you caramelize those onions until they're sweet and golden, then finish everything with a bright lemon butter sauce that makes the whole dish sing. It's simple enough for a Tuesday night but impressive enough to serve guests.
Ella x
Ingredients
- 4mahi mahi fillets(6 oz each, skin removed)
- 3 largeyellow onions(thinly sliced)
- 4 tablespoonsextra virgin olive oil
- 3 tablespoonsbutter
- 3 tablespoonsfresh lemon juice
- 4fresh thyme sprigs
- 2garlic cloves(minced)
- 1 teaspoonsea salt(divided)
- ½ teaspoonblack pepper(divided)
- 118 mlwhite wine(dry)
- 1 teaspoonlemon zest
- 2 tablespoonsfresh parsley(chopped)
Detail level
Instructions
- 1
Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the sliced onions and cook for 25-30 minutes, stirring occasionally, until deeply caramelized and golden brown. Season with half the salt and pepper. Transfer to a plate and set aside.
Tip: The key to perfect caramelization is patience and low heat—resist the urge to turn up the temperature.
- 2
While the onions cook, preheat your oven to 400°F (200°C). Pat the mahi mahi fillets dry with paper towels and season both sides with remaining salt and pepper.
Tip: Drying the fish ensures a better sear and prevents it from steaming during roasting.
- 3
In the same skillet, heat the remaining 2 tablespoons of olive oil over medium-high heat. Once shimmering, carefully place the mahi mahi fillets in the pan and sear for 2-3 minutes per side until golden, then remove and set aside.
Tip: A quick sear develops a flavorful crust without cooking the fish through.
- 4
Reduce heat to medium and add minced garlic to the skillet, stirring constantly for 30 seconds until fragrant. Pour in the white wine and lemon juice, scraping up any browned bits from the bottom of the pan.
Tip: Deglazing the pan captures all the flavorful fond left behind from searing.
- 5
Return the seared mahi mahi to the skillet, nestling each fillet among the pan sauce. Top each fillet with caramelized onions and place a sprig of fresh thyme on each one.
Tip: Arranging the onions on top of the fish helps infuse extra flavor as they roast.
- 6
Transfer the skillet to the preheated oven and roast for 10-12 minutes until the fish is opaque and flakes easily with a fork.
Tip: The internal temperature should reach 145°F (63°C) for perfectly cooked mahi mahi.
- 7
Remove the skillet from the oven and place it over medium heat. Stir in the butter and lemon zest, swirling gently until the butter melts and creates a silky sauce. Taste and adjust seasoning as needed.
Tip: Finishing with cold butter creates a luxurious emulsified sauce without breaking.
- 8
Plate the mahi mahi fillets and spoon the pan sauce and caramelized onions around each piece. Garnish with fresh parsley and serve immediately with roasted vegetables or rice.
Tip: Serve immediately while the fish is still warm and the sauce is silky.
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