Hash Brown Potato and Egg Bake

1/2 lb. bacon, chopped
1 medium onion, chopped (1/2 cup)
1- 30oz. bag frozen country-style shredded hash brown potatoes, thawed, patted dry
2 cups shredded cheddar cheese (8 oz)
1/4 cup grated Parmesan cheese
9 large eggs
1&1/4 cups milk
1-8oz. container sour cream
1 tsp salt
1 tsp ground mustard
1/4 tsp pepper
1/2 cup cornflake crumbs or panko bread crumbs
2 TBSP butter or margarine, melted

Heat oven to 350.  Spray 9x13 glass baking dish with cooking spray.  In 10-inch skillet, cook bacon and onion over meduim-high heat about 10 minutes, stirring occasionally, until bacon is crisp and onion is tender; drain on paper towels.

In large bowl, toss bacon mixture, potatoes, and cheeses.  Spoon into baking dish.  In same bowl, beat eggs, milk, sour cream, salt, mustard, and pepper with fork or wire whisk until well-blended.

Bake uncovered for 35 minutes.  In small bowl, toss crumbs and butter.  Sprinkle over casserole.  Bake 10 to 15 minutes longer or until knife inserted in center comes out clean.