Adding the ingredients in the right order is the secret to this recipe's success; the ones that take longest to cook go in first. Use the broth on the side to dip your seafood and nice thick chunks of french bread.
Combine onions, garlic, pale ale, and water in a 16-quart stockpot. Add potatoes, chorizo, and 1 tablespoon salt. Bring to a boil. Add lobsters; cook over high heat, covered, for 15 minutes. Add clams and corn; cook, covered, for 6 minutes. Add mussels and shrimp; cook, covered, until clams and mussels open and shrimp are cooked through, 4 to 8 minutes.
Remove seafood, corn, potatoes, and chorizo using tongs, and transfer to large platters or rimmed baking sheets. Discard and any unopened clams and mussels. Strain liquid through a sieve into a bowl; add butter, swirling to melt. Squeeze lemons over clambake.