Boil onions until semi-soft. Steam broccoli enough to dethaw, but don’t cook all the way. Melt 1 ½ sticks of butter in large sauce pan. Sprinkle flour into pan and cook on medium heat, add cream cheese, salt, pepper and garlic powder and cook until bubbly. Whisk in milk and cook until thick. Mix sauce, broccoli and onions together in large bowl. Pour into 2 casserole dishes (casseroles can be refrigerated overnight, if necessary.).
Bake at 350 degrees for 30 minutes. Mix bread crumbs, 1 ½ sticks of melted butter and Parmesan cheese together in separate bowl and spread over casserole. Bake another 15 minutes.