1. In medium saucepan cook onion in 1 tablespoon butter until tender. Stir in garlic. Cook and stir for 30 seconds. Stir in soup, milk, mustard and pepper. Set aside.
2. In 12 x 8 x 2-inch baking dish coated with cooking spray layer half of the potatoes. Drizzle with half of the soup mixture. Sprinkle with 2 tablespoons of the Parmesan cheese. Top with remaining potatoes and remaining soup mixture. Tightly cover with foil. Bake at 325°F for 1 1/2 hours or until potatoes are nearly tender.
3. Meanwhile, in small bowl toss together remaining Parmesan cheese, SUNSHINE CHEEZ-IT Original snack crackers and 1 tablespoons butter.
4. Carefully, remove foil from potatoes. Sprinkle with cracker mixture. Bake, uncovered, at 325°F for 15 minutes more or until potatoes are tender. Let stand for 10 minutes.