Keywords: casserole
Preheat oven to 350 degrees. In a large skillet, cook onion in butter until opaque. Stir in flour. Whisk in milk and cook, stirring constantly until thickened. Stir in salt, pepper, eggs and asparagus. Put into a 2 quart casserole. Top with cheese and crumbs. Bake for 30 minutes, until hot and bubbly.