For the Cream of Mushroom Soup:
- 4 tablespoons butter
- 1 white onion, diced
- 4 cloves garlic, minced
- 1½ pounds mushrooms, sliced
- 4 teaspoons thyme, dried
- 1 teaspoon kosher salt
- 1 teaspoon black pepper, coarse ground
- ½ teaspoon xanthan gum
- 4¼ cups beef broth
- 2 tablespoons sherry cooking wine
- 1 cup heavy cream
For the Casserole:
- 1 tablespoon olive oil
- 2 yellow onions, thinly sliced
- 1 pound green beans, ends removed, and cut in half