Wash and trim the green beans and blanch them briefly in salted boiling water until just tender. Drain and either put them in an ice bath to cool or run cold water over them, then drain again and set aside. Blot to dry off the excess water.

In a large skillet, sauté the onion, garlic, and mushrooms in butter over medium heat until soft.

Sprinkle in the gluten free flour slowly while stirring until completely combined.

Slowly whisk in the milk then the broth until smooth.

Simmer the sauce until thickened, then season with salt and pepper and add the cheese.

Meanwhile, rip or chop the bread into pieces.

Combine the green beans, sauce, and bread and stir thoroughly.

Transfer everything to a baking dish and bake until hot and lightly golden on top, about 20 minutes.

Take out the casserole, set the oven to broil, and top with the remaining cheese and any optional toppings above in the swaps/variations.

Broil for 1-3 minutes or until the cheese is melted, checking it every minute. Serve warm!