Zip sauce is a sauce served with beef in Detroit area restaurants. It's made of one part "Flavor Glow" to one part clarified butter, salt and pepper to taste.
You can now buy Zip Sauce by the bottle! See here:
"Flavor Glow" is a gravy base. It's generally sold only to restaurants, but this may be a source:
1-800-792-0816, Ext. 113