low country boil recipe

Ingredients: 4 quarts water 1/4 cup Old Bay seasoning 1 tablespoon salt 1 lemon, halved 2 pounds small red potatoes 4 ears of corn, husked and cut into halves 1 1/2 pounds smoked sausage, cut into 1-inch pieces 2 pounds large shrimp, deveined (leave shells on for flavor) 1 pound crab legs (optional) 1 onion, quartered