Roux is necessary to thicken and give body to sauces. Put one
tablespoon of flour and one of butter into a saucepan and cook until
the flour has lost any raw taste. Then put the saucepan on the back of
the stove and add slowly the stock or milk, one cup for every
tablespoon of butter or flour, and stir until smooth. For white sauces
take care the flour does not color; for dark sauces let it brown, but
take care it does not burn.