Roux is a base sauce in international cuisines, originally French, composed of varying ratios of flour and fat (usually butter), useful for making sauces, and for thickening soups or gravies. The benefits of using a roux include:It does not have to be cooked very long to remove a floury taste, clumps of flour are removed, and it creates unique flavors. It can be cooked to different degrees:
- white roux
- blonde roux
- brown roux
- dark/brick roux
- burnt roux
depending upon the intended use, and a darker roux (one that has been cooked longer) will also be thicker and have more flavor, but will have less thickening power.
- Melt the butter in a thick-bottomed sauce pan over medium heat, then add flour.
- Mix well and cook to desired color, stirring constantly to prevent burning. This may well take up to twenty minutes.
Oven-Made Roux 
Some people find it easier to finish a roux in the oven so as not to burn it with direct heat.
- 1 part fat
- 1 part by weight flour
Preheat oven to 400°F (205°C). Heat the oil in a skillet for 10 minutes on medium-high. Stir constantly for 15 minutes until roux starts to brown. Place the skillet in the oven and cook for 1 hour stirring every 15-20 minutes. Reduce heat to 350 and cook for an additional stirring every 15-20 minutes until your roux reaches the desired doneness. The roux may be stored in the freezer in an airtight container indefinitely.
Notes, tips and variations 
- Depending upon how you plan to use your roux, you may need to add the sauce's other ingredients before the roux is fully cooked.
- One way to use a roux, is to add liquid to it, stirring it in as you go. Don't go the other way, adding the roux to the liquid, as you will get lumps. Once enough liquid has been added to the roux (you'll know), you can safely add it back into another liquid.
- A good roux will have a slight shine to it, and neither the texture nor the taste of the flour will be apparent.
- When making a dark roux, switching from butter to an oil with a high smoke point (such as soybean oil or Canola oil) will allow for a higher cooking temperature, decreasing cooking time. Keep in mind that different fats will give the roux a somewhat different taste.
Escoffier on Roux 
White Roux (Roux blanc) 
Same quantities as for brown or pale roux, but the time of cooking is limited to a few minutes, as it is only needed, in this case, to do away with the disagreeable taste of flour which is typical of those sauces whose roux has not been sufficiently cooked.
Pale Roux (Roux blond) 
The quantities are the same as for brown roux, but cooking must cease as soon as the colour of the roux begins to change, and before the appearance of any colouring whatsoever. The observations I made relative to brown roux, concerning the thickening element, apply also to pale roux.
Brown Roux (Roux brun) 
Quantities for making about one pound:
- 8 ozs. by volume clarified butter
- 8 ozs. by weight flour
Preparation.—Mix the flour and butter in a very thick saucepan, and put it on the side of the fire or in a moderate oven. Stir the mixture repeatedly so that the heat may be evenly distributed throughout. Brown roux is known to be cooked when it has acquired a fine, light brown colour and when it exudes an odour resembling that of the hazel-nut, characteristic of baked flour.
It is very important that brown roux should not be cooked too rapidly. When cooking takes place with a very high heat in the beginning, the starch gets burned within its shrivelled cells. The binding principle is thus destroyed, and double or treble the quantity of roux becomes necessary in order to obtain the required consistency. But this excess of roux in the sauce chokes it up without binding it, and prevents it from clearing. At the same time, the cellulose and the burnt starch lend a bitterness to the sauce of which no subsequent treatment can rid it.
- Auguste Escoffier (1907), Le Guide culinaire