An equal mix of all-purpose flour and fat, such as butter, oil or animal fat.
In a pan over moderate heat, melt and blend butter
or other fat with flour. How long you cook roux before
adding liquids depends on what you are making. For
example, for dark gravy you would cook until rich
brown in colour. For white sauce, cook it just a few
minutes, until still light in colour. 1 Tbsp. flour mixed
with 1 Tbsp. of butter or other fat should yield enough
roux to thicken 3/4 to 1 cup of warm liquid. To avoid
lumps forming, slowing whisk liquid into the
roux and simmer until mixture thickens.