While beef is resting, remove all but about 2 tablespoons of fat from roasting pan. Add shallots to pan and place roasting pan on stove top over medium heat. Sauté shallots for about 2 minutes. Unwrap garlic and carefully squeeze out roasted garlic into shallot mixture (discard garlic skins). Add wine, horseradish sauce, bay leaf, gf beef stock and remaining tablespoon of thyme; bring to a boil, scraping up any browned bits on bottom of pan. Mash garlic, with a spoon, against bottom of pan, until mixture is reduced by 1/2, about 5 minutes. In a small bowl, whisk gf flour with 1/4 cup water until smooth. Gradually add flour mixture to sauce, stirring constantly. Bring sauce to a boil and cook, stirring constantly until reduced to about 2 cups. Whisk in butter until sauce is blended. Pour sauce through a fine sieve, pressing hard on solids. Adjust seasonings to taste with salt and freshly ground black pepper.
This recipe is great with a prime rib or other beef roast.