Ingredients

  • 2/3 cup lightly packed flat-leaf parsley leaves
  • 3 tablespoons drained capers
  • 1 clove garlic, smashed
  • 4 teaspoons lemon juice
  • 1 teaspoon anchovy paste
  • 1/2 teaspoon Dijon mustard
  • 3/4 teaspoon salt
  • 1/4 teaspoon fresh-ground black pepper
  • 1/2 cup plus 1 tablespoon olive oil
  • 4 tuna steaks, about 1 inch thick (about 2 pounds in all)
  • 1 avocado, cut into 1/2-inch chunks

Method

  • Put the parsley, capers, garlic, lemon juice, anchovy paste, mustard, 1/2 teaspoon of the salt, and 1/8 teaspoon of the pepper into a food processor.
  • Pulse to chop, six to eight times.
  • With the machine running, add the 1/2 cup oil in a thin stream to make a coarse puree.
  • Leave the sauce in the food processor and, if necessary, pulse to re-emulsify just before serving.
  • Heat a grill pan or heavy cast-iron pan over moderately high heat.
  • Rub the tuna steaks all over with the 1 tablespoon oil.
  • Sprinkle with the remaining 1/4 teaspoon salt and 1/8 teaspoon pepper.
  • Cook the fish for 3 minutes.
  • Turn and cook until done to your taste, 3 to 4 minutes longer for medium rare.
  • To serve, top the tuna steaks with the avocado and drizzle with the sauce.