- Preheat oven to 350˚. Butter a 9×9-inch baking dish. 
- Bring cottage cheese, mascarpone, sharp cheddar and milk to room temperature before processing. Place cottage cheese and mascarpone in a food processor; blend until smooth. Add milk, mustard, hot sauce, nutmeg, salt and pepper. Blend until fully mixed. 
- Add cheddar cheese and blend until fully combined. The mixture will be very thick. 
- Make broth: Bring 2 cups water to a boil with all broth ingredients except lobster. Add lobster. Cook 7 minutes, until lobster is pink and curled slightly. Remove lobster from pan; set aside to cool. Continue to boil the liquid until it is reduced to 3/4 cup. Drain lobster broth, keep hot, and set aside. 
- Remove lobster from shell, and cut into large chunks. 
- Place cheese mixture and lobster in a mixing bowl. Add enough lobster broth to thin the sauce to the consistency of pancake batter. 
- Boil 6 cups water; add pasta and salt. Cook for about 6 minutes. The pasta should be undercooked. Drain, and add to the cheese sauce. The hot pasta will melt the sauce. Stir well. Add more lobster broth if sauce is too thick. 
- Transfer shells and sauce to baking dish. Top with breadcrumbs. Cover and bake for 20–25 minutes until heated through.