In a large saucepan or pot, combine 2 liters water, 2 tablespoons kosher salt, juice of 1/2 lemon (reserve the other half for serving), 2 bay leaves and 1 tablespoon black peppercorns. Bring to a rolling simmer over medium-high heat.

Poach shrimp

When the poaching liquid reaches a gentle simmer (not a hard boil), add the shrimp in a single layer. Cook until shrimp are opaque and just firm, about 2 to 3 minutes depending on size. As soon as they turn pink and curl, remove immediately with a slotted spoon.

Shock shrimp

Prepare a large bowl with 4 cups ice and 1 cup cold water. Transfer the cooked shrimp to the ice bath to stop cooking and chill fully, about 5 minutes. Keep the poaching liquid warm off the heat if you want to reuse or discard it.

Drain and chill

Drain the shrimp well on a paper towel-lined tray, pat dry gently, then refrigerate uncovered for at least 15 minutes to firm and chill further. Leave tails on for presentation.

Cocktail Sauce

In a small bowl, whisk together 3 tablespoons ketchup, 1 tablespoon prepared horseradish (mild), 1 teaspoon Worcestershire sauce, 1 tablespoon fresh lemon juice, 1 teaspoon hot sauce if using, 1 teaspoon salt and 1 teaspoon freshly ground black pepper until smooth. Taste and adjust: add more horseradish for heat or more lemon for brightness. Chill until service.

Atomic Horseradish Garnish

Stir 1 tablespoon 'atomic' prepared horseradish with 1/2 teaspoon lemon zest. Place in a small ramekin so diners can add an extra kick to their shrimp and sauce. Label as very spicy.

To Serve

Pile crushed ice on a serving platter or individual cocktail glasses. Arrange chilled shrimp over the ice in a ring or stacked presentation, tails out for easy picking. Place a bowl of cocktail sauce in the center and a small ramekin with the atomic horseradish nearby. Garnish with lemon wedges and parsley. Serve immediately.

If preparing ahead: keep shrimp chilled on ice and cover loosely with plastic. Keep sauces refrigerated until serving; bring out just before plating.