Heat 1/2 cup butter in a 13- x 9-inch baking dish in a 350° oven 5 to 6 minutes or until melted.
Spread hash browns over butter in dish; top with vegetables. Stir together soup and next 4 ingredients; spread over vegetables.
Heat remaining 1/4 cup butter in a saucepan over low heat until melted.
Stir together crushed cornflakes and 1/4 cup melted butter; sprinkle over casserole.
Bake at 350° for 45 minutes.
NOTE: For testing purposes only, we used Bird's Eye Frozen Broccoli, Green Beans, Pearl Onions, and Red Peppers for the frozen mixed vegetables.