Step 1

Place corn in a single layer on a large plate; freeze until ready to use, about 1 hour.

Step 2

Meanwhile, add water to a large (16-quart) stockpot. Squeeze juice from lemon halves into water, removing and discarding seeds; add squeezed lemon halves, onions, jalapeños (if using), Old Bay, salt, cayenne, garlic heads, and bay leaves. Cover and bring to a boil over high. Add potatoes. Cover pot, and return to a gentle boil over high. Uncover, and boil, undisturbed, for 15 minutes. Add clams and sausage. Cover pot, and return to a gentle boil over high. Uncover, and boil, undisturbed, for 5 minutes. Remove from heat.

Step 3

Add crab legs, shrimp, and frozen corn to stockpot, using tongs to incorporate them into the broth. Cover pot, and let mixture stand, undisturbed, 15 minutes.

Step 4

Meanwhile, make the Old Bay Butter Sauce: Bring water to a boil in a medium saucepan over high. Reduce heat to low; gradually add butter pieces, whisking until mixture is emulsified and thickened (do not let sauce boil). Remove from heat; stir in parsley, Old Bay, lemon juice, hot sauce, Worcestershire, and cayenne and transfer to a sauceboat or small serving bowl.

Step 5

Working in batches, drain the seafood boil in a colander, using tongs to help transfer ingredients to the colander and then to a serving platter. Serve the seafood boil alongside the warmed Old Bay Butter Sauce.