Lobster Mac And Cheese

Name: Lobster Mac And Cheese
Ingredients: 2 1 1/4-pound live lobsters; 3 tablespoons unsalted butter; 1 shallot, minced; 2 to 3 tablespoons cognac; 1 cup shrimp stock; 1/2 cup heavy cream; Juice of 1/2 lemon; 1 sprig tarragon, roughly chopped; 4 cups heavy cream; 1/2 cup finely grated Parmesan cheese; 2 tablespoons Dijon mustard; 2 teaspoons Worcestershire sauce; 1 teaspoon hot sauce (such as Tabasco); Kosher salt and freshly ground pepper; 3 to 3 1/2 cups grated Gruyère cheese; 1 pound elbow macaroni