Step 1

Prepare the following, adding each to the same small bowl as you complete it: Finely grate the zest of 1 small lemon (about 1 teaspoon). Juice the lemon until you have 2 tablespoons. Mince 2 garlic cloves. Rinse 1 tablespoon capers well under cold running water, if salt-packed, to remove salt.

Step 2

Cut 4 tablespoons cold unsalted butter into 4 pieces. Coarsely chop the leaves and tender stems of 2 fresh parsley sprigs (about 1 tablespoon). Pat 4 (4 to 6-ounce) skinless halibut fillets dry with paper towels. Season all over with 1 teaspoon kosher salt and 1/4 teaspoon black pepper.

Step 3

Heat 2 tablespoons olive oil in a large cast iron or nonstick skillet over medium-high heat until just starting to smoke, 2 to 3 minutes. Add the halibut and sear undisturbed until well browned on the bottom and the sides are cooked just past halfway up the fillets, 4 to 5 minutes. Reduce the heat to medium, flip the fillets, and cook until just cooked through and the flesh flakes easily, 3 to 5 minutes more. Transfer to a serving platter or individual plates.

Step 4

Reduce the heat to medium-low. Add the lemon juice mixture and scrape up any browned bits from the bottom of the pan with a wooden spoon. Add the butter one piece at a time, waiting until each piece is almost completely melted before adding the next.

Step 5

Remove the pan from the heat and stir in the parsley. Taste and season with salt and pepper as needed. Pour over the halibut and serve immediately.