Using a metal saucepan, heat the butter and flour until the roux is a dark brown. Stir it constantly or it will burn. Add a small amount (1/4 cup) of the stock/dripping mix, stirring as it splatters and tries to burn you. Add the rest of the liquid and stir until it boils, then let it boil for one minute. Remove from the heat, it will thicken as it cools.