Melt the butter in a small saucepan. Add the diced mushrooms and cook for 5-6 minutes, until liquid is mostly reduced.
4 tablespoons butter, 2 cups finely diced baby Bella mushrooms
Add the flour and mix it together
1/2 cup all-purpose flour
Add the chicken broth and stir to combine.
2 cup chicken broth
Mix in milk and then the seasonings. Whisk continuously and bring to a gentle boil. Stir continuously while it bubbles for about 4-6 minutes, it will thicken and reduce. Remove from heat.
2 cup whole milk, 1 1/4 teaspoon garlic powder, 1 ¼ teaspoon onion powder, 1 teaspoon salt, 1/2 teaspoon black pepper, 1/2 tsp dried parsley flakes
It will continue to thicken as it cools. Allow cooling for about 5-10 minutes.
In a large bowl, mix together homemade cream of mushroom soup, green beans, cheese and milk, and half of the onions.
24 ounces frozen green beans, 3/4 cup shredded cheddar cheese, ½ cup milk
Pour in a 9 x13 inch baking pan. Bake at 350 degrees for 25 minutes or until bubbly.
Top with remaining french fried onions and bake for 5 more minutes. You will know it is finished when the green bean mixture is bubbly, and the onions are crispy and starting to brown.