In a medium saucepan combine 4 cups water, 1 tablespoon kosher salt, 4 lemon slices, 1 bay leaf, and 6 black peppercorns. Bring to a gentle simmer over medium heat until salt dissolves and liquid is fragrant, about 3–4 minutes.

Cook shrimp

Add the 4 jumbo peeled and deveined shrimp to the simmering liquid in a single layer. Return liquid to a gentle simmer (do not boil hard) and cook until shrimp are opaque and just curled, about 2–3 minutes depending on size. Jumbo shrimp may need up to 3 minutes; watch carefully to avoid overcooking.

Shock shrimp

Immediately transfer shrimp with a slotted spoon to a bowl filled with 2 cups ice and enough cold water to cool quickly. Let shrimp chill in the ice bath until completely cooled, about 5 minutes. This stops cooking and firms texture.

Drain and chill

Drain shrimp on paper towels. Keep chilled until serving. You may refrigerate covered up to 2 hours.

Cocktail Sauce

In a small bowl combine 1/2 cup ketchup, 2 teaspoons prepared horseradish, 1 teaspoon fresh lemon juice, 1/2 teaspoon Worcestershire sauce, and 1 dash hot sauce if using. Stir until smooth. Taste and adjust heat by adding more horseradish or hot sauce; season with a pinch of salt and freshly ground black pepper to taste.

Garnish & Serve

Arrange 4 chilled shrimp on a serving plate or in individual cocktail glasses over a bed of crushed ice if desired. Place a small bowl of cocktail sauce in the center or alongside. Garnish with lemon wedges and a sprinkle of chopped parsley. Serve immediately so shrimp are cold and sauce is chilled.