Sauce Châteaubriand Adapted from The Escoffier Cookbook
The veal gravy in the ingredient list can be made by thoroughly mixing 1 tablespoon of corn starch into a quarter cup of cold water, then pouring it into 2 cups of simmering veal stock, and stirring until the mixture is smooth and thickened. Do not allow it to boil.
Put shallots, thyme, bay leaf, mushroom peelings, and white wine into a saucepan. Reduce the wine almost entirely. Add veal gravy and reduce again until the liquid only measures 1/2 cup. Strain the sauce through cheesecloth.
Mix the butter and flour thoroughly in a bowl. Add the parsley, lemon juice, and salt and pepper, and mix until uniform.
Return the sauce to the pan, add the butter mixture and tarragon, and finish over low heat until the taste of uncooked flour disappears. Do not allow to boil.
Serve with châteaubriand or other grilled fillet of beef.