Instructions: Saute onion in butter in a large skillet just until tender. Add ground beef; cook until browned, stirring to crumble meat. Drain excess fat. Add spaghetti sauce, tomatoes, mushrooms, and garlic salt to meat mixture; stir well, and simmer 20 minutes.

Cook shell pasta according to package directions except reduce salt to 1 1/2 teaspoons; drain.

Place half of macaroni in a deep 4-quart greased casserole; layer with half of meat sauce, half of provolone, and half of sour cream. Repeat layers and top with mozzarella cheese. Cover and bake at 350 degrees F. for 30 minutes; uncover and bake 15 minutes.

Yield: 12 servings.

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