How to Make It
Preheat oven to 400°F. Slice 1 orange and 1 lime into 1/4-inch thick rounds.
Place salmon, skin side down, on a parchment-lined rack set inside a rimmed baking sheet. Brush salmon with melted butter. Sprinkle with 1 1/2 teaspoons of the salt and 1/2 teaspoon of the pepper. Cover loosely with aluminum foil. Roast in preheated oven 25 minutes. Uncover and arrange citrus slices over salmon in an artful pattern. Return salmon to oven, and roast at 400°F until fish flakes easily with a fork, about 20 minutes.
Meanwhile, juice remaining oranges and limes (making 1 1/4 cups juice). Strain juice into a stainless-steel saucepan. Bring to a boil over medium-high, reduce heat to medium, and simmer until reduced to about 2/3 cup, about 10 minutes. Remove from heat. Stir in cubed butter, 2 tablespoons of the dill, and remaining salt and pepper.
Place salmon on a platter; sprinkle with remaining dill. Serve with sauce.