Grilled Tuna With Cilantro Butter

Ingredients 1/4 cup plus 2 tablespoons butter, softened 1/4 cup fresh cilantro leaves, loosely packed 2 tablespoons plus 2 teaspoons peeled, minced ginger root, divided 1 teaspoon minced garlic 6 (4-ounce) tuna steaks (3/4 inch thick) 1/2 cup firmly packed brown sugar 1/2 cup soy sauce 1/2 cup water 1/4 cup dark sesame oil 2