You can use any lean, firm fish in place of grouper.
Cook first 3 ingredients in a small saucepan over medium heat 5 minutes or until butter is melted.
Place fish fillets on a lightly greased rack in a broiler pan. Drizzle evenly with lemon juice, and brush with tarragon sauce mixture.
Broil 6 inches from heat (with electric oven door partially open) 10 minutes on each side or until fish flakes with a fork, basting occasionally with remaining tarragon sauce mixture.