Preheat the oven 350 degrees.
Bring a large pot of water to a boil, add salt and green beans. Cook 5-7 minutes. Remove to an ice bath. Cool, drain thoroughly.
In a medium saucepan, melt the butter, add the onions and saute until soft, about 5 minutes.
Add the garlic and saute another minute.
Add the mushrooms, saute until moisture is releasing about 4-5 minutes. Sprinkle the flour over and stir, cook another 1-2 minutes to remove the flour taste.
Add the stock, fresh thyme, bay leaf, Worcestershire, salt, and pepper. Simmer for about 3 minutes.
Reduce the heat to medium-low, add the heavy cream, stir and continue simmering until the sauce thickens to your desired consistency. Usually 10-15 minutes. Remove the bay leaf and thyme sprigs from the sauce.
Pour the sauce over the green beans, stir to evenly coat. Pour into a 9x13 baking dish. Sprinkle the French fried onions over the top evenly.
Bake for 15-20 minutes, until browned and bubbling.
Let rest at least 5 minutes before serving.