Preheat oven to 350 degrees F. In a large skillet cook bacon over medium heat until crisp, turning once. Drain bacon on paper towels; crumble. Reserve bacon drippings in skillet.
Cook onion in reserved bacon drippings for 5 to 8 minutes or until onion is tender and golden brown. Set aside.
Cook elbow macaroni according to package directions. Drain and place in a 1-1/2-quart casserole. Add the crumbled bacon, onions, 1-1/2 cups of the mozzarella cheese, the blue cheese, half-and half, and pepper. Toss gently to combine.
Bake, uncovered, for 20 minutes. Stir gently. Top with the remaining mozzarella cheese. Bake for 10 minutes more or until top of casserole is brown and bubbly. Let stand 10 minutes.