PREPARATION: Bring 4 quarts of water to boil in a 6to 8-quart soup kettle. Add lobster , cover and boil for about 10 minutes. Remove and reserve the shells and carcass for stock. Cut lobster meat into 2-inch pieces. (Can wrap and refrigerate meat and shell overnight.) Peel and cut potatoes into 1/2-inch dice. Mince the onion (1 cup). Remove the corn kernels from the cobs (or drain and set aside thawed corn). COOKING AND SERVING: Put the reserved lobster shells and carcass in a large saucepan with the half-and-half. Bring to a boil, lower heat, and simmer 4 minutes. Remove from heat and set aside. Melt the butter in a soup kettle. Add the potatoes, onion and corn kernels and saute over medium-low heat until the onion is translucent, about 5 minutes. Strain the lobster cream over the vegetables, bring to a simmer, and then simmer slowly until the potatoes are tender, 6 to 8 minutes. Stir in the lobster meat, cayenne pepper, salt, and pepper. Simmer just until the lobster meat is hot, about 5 minutes. Ladle into warm bowls and serve with Corn Crisps. Makes 4 servings. [COOKS; Jul/Aug 1988]