Preheat oven to 350 degrees. Bake the bacon until crisp, turning once. Drain bacon on paper towels; crumble. Drain bacon drippings into saute pan.
Cook onion in bacon drippings for 8 to 10 minutes or until onion is tender and golden brown. Set aside.
In a large saucepan cook macaroni according to package directions. Drain and return to saucepan. Stir in the crumbled bacon, onions, 1-1/2 cups of the mozzarella cheese, the gruyere cheese, cream, and pepper. Toss gently to combine. Spoon into a 1-1/2-quart casserole.
Bake, uncovered, in a 350 degree F ovenfor 20 minutes. Stir gently. Top with the remaining mozzarella cheese and sprinkle with crumbs. Bake for 10 minutes more or until top of casserole is brown and bubbly. Let stand 10 minutes.