In a pot melt butter and sauté mushrooms and garlic over medium heat for 5 minutes.
In a small bowl combine 2 Tbsp corn starch with 1/4 cup chicken broth.
Add remaining chicken broth, heavy cream, salt, pepper, thyme, and corn starch slurry to pot and cook cover medium heat until thickened. If the mixture is not thickening enough, combine remaining corn starch with 1/4 cup water and add to pot. Set aside.
Remove ends of the green beans and cut into smaller pieces.
Add green beans to a baking dish, top with cream of mushroom, and 1 cup of fried onions. Mix to combine.
Bake for 30 minutes. Remove from oven and top with remaining fried onions. Bake an additional 5 minutes and enjoy!