Roux (French for red) is a cooked preparation of butter and flour used for thickening gravy, sauces, and soups. The proportions of butter and flour are one ounce of butter and half an ounce of flour to one cup of liquid for sauces, and one pint of liquid for soups; by measure two level tablespoonfuls, each, of butter and flour to one cup, or one pint of liquid. While these are the ordinary proportions, more flour, even a full ounce, for an ounce of butter is occasionally required, as when making sauce for croquettes and similar mixtures. And also when making a brown roux, or roux proper, as the flour in browning loses some of its thickening qualities. To prepare, melt the butter; when bubbling add the flour, mix well and leave on a slow fire, stirring occasionally until it becomes of a reddish brown, or mahogany color.

This is roux, but in cookery we speak of it as brown roux. When the flour has cooked in the bubbling butter just long enough to burst the starch cells, rather less than five minutes, and without taking color, the preparation is called blonde roux. When a more highly flavored roux is desired, cook a "faggot" with a slice of onion in the butter before adding the flour. Cool the roux before adding a hot liquid; a cold liquid may be added at once. Roux may be prepared and set aside for future use. This may be of advantage in the case of brown roux, but certainly it is not called for in the case of the blond, as it is but five minutes' work to prepare the latter.