You'll never make the Campbell's soup version again if you'll go with this instead. Sure, it's more work--but so, so good. Yes, heavy cream and butter. Yes, fresh mushrooms and fresh green beans. Go for it!
Process bread slices with butter, mix with French-fried onions, salt and pepper. Set aside.
Heat oven to 425. Blanch and drain beans, using salted water. Melt butter, saute mushrooms and garlic, then stir in flour. Stir in broth and bring to a boil, stirring, then add cream and simmer until thickened. Season with salt and pepper to taste. Add green beans and turn into 13x9 baking dish, sprinkle with topping and bake until top is golden brown and sauce is bubbling, about 15 minutes.
This is actually not that big of a recipe. For a large group, I'd do a 1 1/2-times recipe and put in a 10x13 pan. Baking time may need to be a little longer.
*Although I really like the idea of combining breadcrumbs and French-fried onions, sometimes life goes by a little too fast for that extra step. If you find yourself running out of time, just skip the breadcrumb business and lard on the onions!