Preheat oven to 375 degrees.
In a large skillet set over medium heat, add the butter. Once the butter has melted, add the mushrooms and cook until browned, about 5-7 minutes. Add shallot and garlic, sauté until fragrant, about 1 minute.
Sprinkle in flour, whisk continuously until golden brown. Slowly whisk in the chicken broth, then the cream. Add the salt, garlic, pepper, and parmesan. Bring mixture to a simmer, allow to thicken substantially, about 5 minutes. Add the green beans and continue cooking for an additional 10 minutes.
Meanwhile, in a small skillet set over medium heat, add the 2 tablespoons of butter. Once the butter has melted, add the breadcrumbs and toast until golden brown. Sprinkle over the top of the skillet along with the fried onions.
Place in the oven and bake for 20-25 minutes or until the green beans are cooked throughout and the topping is golden brown in color.