Step 1

Position an oven rack in center of the oven and preheat to 450 degrees F. Line a rimmed baking sheet with aluminum foil and brush with oil.

Step 2

Rinse the salmon fillets with cold water and pat them well with paper towels. Place the fillets, evenly spaced, in the middle of the prepared baking sheet.

Step 3

Bake for 8 minutes; remove the baking sheet from the oven and season the tops of the fillets with 1 teaspoon salt. Continue to bake until the salmon is opaque throughout and the insides flake easily when you insert a paring knife between the layers, 5 to 8 more minutes, depending on the desired doneness (cook until bright pink for rare, pale pink for medium and orange for well done).

Step 4

Meanwhile, whisk together the lemon juice and mustard in a large bowl. Add the butter and a pinch of salt and whisk until the sauce is smooth. Top each salmon fillet with some sauce.