Butter-Roasted Halibut with Asparagus and Olives

Our best tip for cooking fish for a crowd? Slow-roast a single large fish fillet instead of making several small ones—it ensures that the fish is buttery and delicious. Vegetables that are best served crisp-tender are a great accompaniment because they'll be perfectly cooked by the time the fish is finished.

 

2 bunches asparagus, trimmed, halved lengthwise if thick, divided

6 Tbsp. unsalted butter

7 Tbsp. extra-virgin olive oil, divided

1 tsp. Aleppo-style pepper

2½ lb. skinless halibut, salmon, or arctic char fillet

Kosher salt, freshly ground pepper

2 bunches ramps or scallions, trimmed

¾ cup Castelvetrano olives, pitted, torn

¼ cup finely chopped chives

¼ cup fresh lemon juice

2 Tbsp. coarsely chopped tarragon, plus leaves for serving

Boiled small waxy potatoes and lemon wedges (for serving)

 

Preheat oven to 325°. Thinly slice one-quarter of asparagus into coins and place in a medium bowl; set aside.

 

Heat butter and 2 Tbsp. oil in a small saucepan over medium. As soon as butter is melted, add Aleppo-style pepper and remove from heat.

 

Season fish with salt and black pepper on both sides and place on a rimmed baking sheet. Scatter ramps and remaining asparagus around fish; season with salt and black pepper. Pour butter mixture over fish and vegetables. Give vegetables a toss to evenly coat. Roast, undisturbed, until fish is just opaque in the center and asparagus is bright green and tender, 15–25 minutes, depending on the thickness of your fillets.

 

Toss olives, chives, lemon juice, 2 Tbsp. tarragon, and remaining 5 Tbsp. oil with reserved asparagus; season with salt and black pepper.

 

Transfer fish to a platter; top with ramps and asparagus. Spoon some olive mixture over, then scatter tarragon leaves over. Serve with potatoes, lemon wedges, and remaining olive mixture alongside.