Cook Medium Pasta Shells (0.5 pound) 1 minute short of al dente according to package directions. Pour pasta into a colander and rinse with cold water to stop the cooking. Set aside to drain.
In a food processor, add the Fresh Parsley (1 tablespoon), Bread (1 slice) and Vegetable Oil Cooking Spray (as needed) and pulse until crumbly. Spray an 8" casserole dish with Unsalted Butter (3 tablespoon) and set aside. Preheat the oven to 350 degrees F (180 degrees C).
In a saucepan, melt Butter (1 tablespoon) and whisk in Dry Mustard (1/2 teaspoon), Cayenne Pepper (1 pinch), Kosher Salt (1 teaspoon), Ground Black Pepper (1/4 teaspoon) and All-Purpose Flour (3 tablespoon).
Add Lobster Stock (1 1/2 cup) and whisk. Add Milk (1 cup) and Cream (1/2 cup). Heat the mixture just to the boiling point, whisking continuously.
Remove the sauce from heat and stir in the pasta. Add the Lobster Chunks (1 1/2 cup), Gruyère Cheese (1 3/4 cup) and Fresh Parsley (1 tablespoon). Stir to combine.
Pour the pasta mixture into the prepared dish. Sprinkle with Breadcrumbs (to taste) and Gruyère Cheese (1/4 cup).
Bake for 15 minutes or until breadcrumbs are lightly browned and casserole is bubbly. Serve and enjoy!