Step 1

Thaw 6 king crab legs, 2 pounds jumbo shrimp, and 3 lobster tails in the refrigerator if frozen, about 36 hours.

Step 2

Halve 2 medium lemons crosswise. Pick the leaves from 8 to 10 fresh parsley sprigs and finely chop until you have about 1/4 cup. Reserve for the sauce and serving.

Step 3

Prepare the following, adding each to the same medium bowl as you complete it: Peel and quarter 1 medium yellow onion. Cut 2 garlic heads in half across the equator to expose the cloves. Cut 14 ounces andouille sausage crosswise into 2-inch pieces.

Step 4

Halve 1 pound baby red potatoes. Shuck 3 ears corn and cut crosswise into 3-inch pieces.

Step 5

Rinse the king crab, shrimp, and lobster tails in cold water, then drain. Cut the lobster tails in half lengthwise, cutting through the shell.

Step 6

Heat 3 tablespoons olive oil in a 7-quart or larger pot over medium heat until shimmering. Add the garlic, onion, and sausage, and sauté, keeping the garlic cut-side-down, until the onions are softened and the garlic is golden-brown, about 3 minutes. Add 4 quarts water, increase the heat to high, and cover. Bring to a boil, 10 to 15 minutes.

Step 7

Add the potatoes, corn, and 1/2 cup of the Cajun or Old Bay seasoning, and stir to combine. Cover and cook until the water returns to a boil. Uncover, add 8 ounces mushrooms if desired, and simmer, adjusting the heat as needed, until the potatoes are fork tender, 10 to 12 minutes.

Step 8

Add the crab legs, lobster, and shrimp, and stir to combine. Turn off the heat, cover, and let sit for 3 minutes. (The seafood will gently cook in the residual heat.) Uncover and reserve 2 cups of the cooking liquid. Drain the seafood and vegetables, then transfer onto baking sheets or directly onto the center of newspaper-lined table.

Step 9

Add 4 tablespoons salted butter and and the parsley to the reserved cooking liquid. When the butter is melted, stir to combine to make the sauce. Pour half of the sauce over the seafood and vegetables. Squeeze the lemon halves over everything and sprinkle with the remaining 1 tablespoon Cajun or Old Bay seasoning. Serve with the remaining sauce for dipping and Tabasco if desired.