Add 1 Tbl. butter, sliced mushrooms, and shallots and sauté for 4-5 minutes. Add the fresh thyme and cook an additional minute. Dust mixture with flour and cook for 1-2 minutes. The mixture will be thick. Gradually stir in beef broth 1/2 cup at a time, allowing mixture to come to a boil in between each addition. Add more broth until desired thickness is achieved. Season with salt and pepper.