Cut two lemons into quarters and slice the remaining lemon into wedges for garnish.
Fill a large pot with 3.5 to 4 quarts of water, add quartered lemons, Old Bay seasoning, smashed garlic, and onion, then bring to a vigorous boil.
Add halved potatoes to the boiling water and cook for 8 minutes.
Add lobster tails and boil for 5 minutes more.
Add clams, crab legs, and corn pieces, boiling for another 5 minutes until clams open.
Stir in shrimp and smoked sausage, boil for 2 to 3 minutes until shrimp turn pink and are cooked through.
Drain seafood, sausage, potatoes, and vegetables, reserving 1 cup of broth.
Melt butter and whisk it into the reserved broth, then pour the buttered broth evenly over the seafood mixture.
Garnish with chopped parsley, lemon wedges, and sprinkle extra Old Bay seasoning as desired before serving hot.