1 lb. ground beef
1 c. chopped onion
1 clove finely chopped garlic
1 sm. can tomatoes (12-14 oz.)
1 sm. can mushrooms (optional)
1 jar spaghetti sauce (28-32 oz.)
1 box med. shells
8 oz. Provolone cheese
8 oz. Mozzarella cheese
8 oz. sour cream

Cook shells according to package instructions. Combine first 6 ingredients and simmer 20 minutes. In large ovenware bowl, put a layer of shells on bottom, then the sauce mixture, then half of the sour cream and then half of the cheese. Repeat process once more. Bake 45 minutes at 350 degrees. Cover with foil for the first 30 minutes, then cook uncovered for the final 15 minutes.