HEAT oven to 400°F.
PAT hash browns dry with paper towels; mix with butter. Press onto bottom and 1 inch up sides of 13x9-inch baking dish sprayed with cooking spray. Bake 20 to 25 min. or until lightly browned.
REDUCE oven temperature to 350°F. Sprinkle ham, then cheese onto bottom of crust. Whisk eggs and milk until blended; pour over cheese.
BAKE 20 to 25 min. or until knife inserted in center comes out clean.