Old School green bean Casserole

 3 (15 oz.) frozen green bean

1/2 cup salted butter 

1 (8 oz.) fresh, sliced Crimini mushrooms 

1 large shallot

6 Tbsp. Fluor

4 cups whole milk 

4 oz. shredded Parmesan cheese 

2 tsp. Salt

1/2 tsp. Black pepper 

1 8 oz. can diced water chestnuts, drained 

1 cup crispy fried onions

Preheat oven to 350.  Squeeze water from the green beans. 

Add 2 tablespoons butter in a Dutch oven over medium-high heat. Add the mushrooms and shallots to the Dutch oven and cook until the mushrooms and shallots are tender and caramelized. When done, Move the mixture to a plate, and add the rest of the butter to the same Dutch oven .

When butter melts over medium heat, add the Fluor, whisk constantly while Fluor cooks, about 1 minute. Slowly add the milk, keep whisking, until it's smooth, keeps cooking and whisking until it thickens and starts bubbling.  Add the cheese, salt, and pepper  whisking until cheese melts.

Add the green beans, mushrooms mixture and water chestnuts, then spoon unto a baking dish (13x9).

Bake until bubbles, about 15 minutes.  Take out of the oven and sprinkle with fried onions, then put back in the oven for another 15 minutes, or until onions are golden brown.