French Onion Green Bean Casserole

Source: http://foodwishes.blogspot.com/2011/11/french-onion-green-bean-casserole-its.html

2 T Butter
3 Onions, Sliced
Salt and Pepper, to Taste
1 T Sherry Vinegar
2lbs Green Beans, Blanched
Salt and Pepper to Taste
4 oz Grated Gruyere Cheese, Divided
2-3 oz Grated Parmesan Cheese
1 C French Fried Onions

White Sauce
2 T Butter
2-1/2 T Flour
2-1/2 C Milk
Pinch of Nutmeg
Pinch of Cayenne
1/4 t Dried Thyme
Salt and Pepper, to Taste

Saute onion in butter with salt and pepper until caramelized. about 20 minutes. De-Glaze with vinegar and set aside. Meanwhile, Blanch green beans in boiling water salted water for 3-4 minutes. Drain green beans very well.

Melt the butter and whisk in the flour. Add the milk, a small amount at a time until all the lumps are out. Add nutmeg, cayenne, thyme, salt, and pepper. Bring to a simmer and cook 2-3 minutes and set aside.

Layer into a sprayed 9x13 casserole dish:

1/2 Onion Mixture
All the Green Beans, Seasoned with salt and pepper
All the White Sauce
1/2 the Gruyere Cheese
Remaining Onion Mixture
French Fried Onions
Remaining Gruyere Cheese
Parmesan Cheese

Bake for about 30 minutes in 375F oven. Let sit 10 minutes.