Thaw shrimp, if frozen. Rinse shrimp; pat dry with paper towels.

Preheat broiler. Using a sharp paring knife, split each shrimp down the back through the shell almost all the way through the meaty portion, leaving the legs intact. Devein shrimp. Loosen shrimp from shell by running knife between shell and shrimp meat. Flatten shrimp with your hand or the flat side of blade. (Or remove shell, leaving tail intact and flatten with hand or knife blade.) Arrange the prepared shrimp, split sides up, in a single layer on a broiler pan.

Meanwhile, in a small saucepan, cook garlic in hot butter until tender. Stir in basil, white balsamic vinegar, and salt.

Brush shrimp with garlic mixture. Broil shrimp 3 to 4 inches from the heat for 5 to 8 minutes or just until the shrimp are opaque. Transfer shrimp to a platter. If desired, surround with watercress or parsley. Makes 8 servings.

Prepare as directed through step 2. Cover and chill for up to 6 hours. Continue as directed in steps 3 and 4.