Preheat the broiler or prepare a charcoal or gas grill. Press the cracked pepper into both sides of the tuna and season with a little salt. Broil or grill 4 inches from the heat for 4 to 6 minutes on each side, until opaque throughout. Cover and keep warm. In a small skillet, melt the butter voer medium-high heat. Add the garlic and cook for 2 to 3 minutes, until lightly browned. Add the tarragon and wine, raise the heat and broil for 4 to 5 minutes, until reduced to 1/2 cup. Spoon the sauce over the tuna and serve immediately.