If using fresh green beans, bring a large pot of salted water to boil while you trim beans. Add beans and cook for 7 minutes. Strain and put beans in a large pot of ice water to halt cooking. If using frozen green beans, thaw in a strainer under hot water and let sit while you prepare the sauce.
Melt Tuscan Herb Flavored Butter in a large skillet. Add mushrooms and sauté until mushrooms release their moisture, about 5 minutes.
Sprinkle with salt, pepper, and flour and stir for 1 minute. Add broth and soy sauce and cook for 5 minutes until mixture thickens.
Add half-and-half, bring back to a boil then reduce heat to a simmer and cook for 10 minutes until thick.
Add beans and ⅓ cup of the French fried onions and spread in a greased 1 ½ quart casserole. Bake for 15 minutes. Remove from oven and sprinkle with remaining onions. Bake for another 5 minutes. Sauce will further thicken as it cools.
