Crunchy Onion Potato Casserole

2 1/2	cups milk
1 1/2	cups water
1/4	cup butter
1	recipe Garlic Mashed Potatoes
1	can (15.25 oz) whole kernel corn, drained
1	cup shredded Cheddar cheese (4 oz)
1	can (2.8 oz) French-fried onions

1.   Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 3-quart saucepan, heat milk, water and margarine to boiling. Stir in contents of both pouches of potatoes (from potatoes box) just until moistened; let stand 1 minute. Stir with fork until smooth. Stir in corn.
2.   Spoon half of potato mixture into dish. Sprinkle with 1/2 each of the cheese and onions. Top with remaining potatoes; sprinkle with remaining cheese and onions.
3.   Bake 10 to 15 minutes or until cheese is melted and onions are golden.