Preheat oven to 350 degrees. Lightly spray casserole dish with cooking spray and set aside.
In a large, deep skillet, melt butter over medium heat. Whisk in flour to create a paste and cook 1 minute. Slowly whisk in milk (and cream). Bring to simmer to thicken sauce and reduce heat immediately. Stir in salt, pepper and nutmeg. Remove from heat.
Coat green beans and half the cooked bacon in the sauce and pour into prepared casserole dish. Top with fried onions and remaining bacon.
Bake for 30 minutes and serve.
**if you don't like the flavor of frozen green beans, try using fresh green beans that have been prepared and steamed OR canned green beans that have been drained and rinsed well.