Ingredients

• 2 lemons, quartered
• 2 bay leaves
• 3 tablespoons kosher salt
• 2 tablespoons whole black peppercorns
• 1/2-3/4 cup crab and shrimp boil seasoning, such as Old Bay, plus more, or 4 (3-ounce) bags Zatarain's Crawfish, Shrimp, and Crab Boil (See Cooks' Note)
• 4 pounds small new potatoes (about 1 1/2" in diameter)
• 2 pounds smoked pork sausage (about 4 links), such as kielbasa, cut into 2" pieces
• 2 sweet or yellow onions, peeled, quartered
• 8 ears of corn, shucked, cut in half
• 4 pounds fresh large shrimp (31–35 count; preferably wild-caught), unpeeled
• 1 cup ketchup
• 2 tablespoons plus 2 teaspoons prepared horseradish
• 2 tablespoons plus 2 teaspoons Worcestershire sauce
• 1 tablespoon fresh lemon juice
• Louisiana-style hot sauce, such as Crystal (to taste; optional)
• 1/4 cup (1/2 stick) unsalted butter, melted
• 2 tablespoons (or more) fresh lemon juice
• Louisiana-style hot sauce, such as Crystal (to taste; optional)
• A large (at least 12-quart) stockpot, preferably with a perforated insert, or 2 large (at least 6-quart) pots

Instructions

1. Fill stockpot with 6 qt. water (if using 2 pots, divide ingredients and water between them). Add lemons, bay leaves, salt, peppercorns, and 1/2 cup seasoning, cover, and bring to a rolling boil. Add potatoes, return to a boil, and cook 7 minutes. Add sausage and onions, return to a boil, and cook 5 minutes. Add corn, return to a boil, and cook until corn is cooked and potatoes are tender when pierced with a knife, about 5 minutes more.
2. Add shrimp and cook (no need to return to a boil), stirring gently, until shrimp turn pink, about 3 minutes. Remove insert or drain through a very large colander.
3. Stir ketchup, horseradish, Worcestershire, lemon juice, and hot sauce, if using, in a medium bowl.
4. Melt butter in a small saucepan over medium-high heat. Transfer to a medium bowl and stir in lemon juice and hot sauce, if using. Taste and add more lemon juice, if needed. Cover and let sit in a warm place.
5. Serve shrimp boil on a newspaper-lined table or large platters. Dust with additional Old Bay, if using. Serve with sauces alongside, if desired.
6. Cocktail sauce can be made 1 week ahead. Transfer to an airtight container and chill.