How to Make It
Heat a grill pan. Brush the fish with 2 tablespoons of the olive oil and season with salt and black pepper. In 2 batches, cook the fish over moderate heat until browned on one side, 3 minutes. Turn the steaks and top each with 1/2 tablespoon of butter. Grill until the fish is just cooked through, 2 minutes longer. Transfer to serving plates.
Meanwhile, in a bowl, mix the remaining 1/2 cup of olive oil with the remaining ingredients and season with salt and black pepper.
Spoon the vinaigrette over the swordfish and serve.