In a medium pan, heat butter and sauté halved mushrooms with salt and pepper to taste over medium-high heat. As an optional step you can deglaze the pan with some brandy or bourbon towards the end. The alcohol will burn off but you'll get a great depth of flavor!
In an 8x8 casserole pan, add milk, salt, pepper, cream of mushroom, green beans, sautéed mushrooms and fried onions then mix together. *You can also mix everything in a large bowl and transfer into your baking dish if you're worried about spilling.
Add cheddar and gouda to the top.
Bake for 20 minutes at 350F, remove from oven and add fried more onions to the top. Put back in to bake for 10-15 minutes or until golden and crispy.
Try deglazing the pan with some brandy or bourbon towards the end. The alcohol will burn off but you'll get a great depth of flavor!
If you prefer to use fresh green beans: remove the top and bottom of each pod. Blanch in boiling water for two minutes and sauté in some butter with salt and pepper to taste to further soften and enhance the flavor.
Hate mushrooms? Don't bother using them! The dish will still taste great.