Cut all beans in half and cook in boiling water until tender. Drain and set aside.

Butter a 2qt baking dish and set aside.

In a large saucepan, sautee bacon until crispy.

Add butter, onion and mushrooms and cook until soft.

In a medium mixing bowl, whisk together milk and cornstarch.

Add the milk to the saucepan, half of a cup at a time and whisk until it thickens.

Add salt and pepper to taste.

Pour the mixture over the green beans. Toss gently to coat.

Pour the mixture into the prepared baking dish. You can cover the dish with saran wrap and refrigerate overnight or bake right away.

Preheat oven to 350 degrees F.

Top with French fried onions and bake for 10 to 15 minutes.

Let sit in room temperature for 10 minutes before serving.