A roux is the perfect mixture chefs use to thicken soup, gravy, sauce and other food products of similar textures. I will show you how to make roux with the roux colors used in the culinary world: white, blond, and brown.
Add the flour to the butter and mix well. Stir constantly while the flour gets cooked - you can make this in 3 colors depending on the sauce or plate you’ll make afterwards. (You want it to gently bubble as it cooks. If it is bubbling too vigorously, turn the heat down.)
For a light colored (white) roux, cook until you get a light color (about 4 minutes).
For a medium (blond) roux, continue cooking until lightly browned (about 7 minutes).
For a dark (brown) roux, cook until brown in color (about 12 to 15 minutes). For an even darker brown you can cook it longer.
You can now use the roux to thicken soups and sauces. See notes below for ratio and liquid amounts.
Notes
The times are approximate and will vary. Note that the time it takes to achieve each roux color is approximate. Watch closely for the color change as you are mixing. Also note that the less flour and fat you use, the quicker it will cook.
Add liquid slowly. When adding a liquid to a roux, it should be added slowly and constantly whisked.
General roux color. The medium (blond) roux is a good general-purpose roux that you can use for gravy.
Roux ratio. Roux ratio is 1:1 fat to flour by weight
Amount to use per 1 cup liquid (use as a general guide):
Darker roux = less thickening power. The darker the roux, the less thickening power it has.
When to add the liquid. If you are using the roux immediately and you just finished this tutorial, this would be the point where you slowly whisk in the liquid you are using and simmer until thickened.
How to tell if it's burnt: You can easily tell because it will be very dark and have a strong, undesirable, burnt smell.
Storage. If you aren't using the roux immediately, you can store it in the fridge for up to 6 months or in the freezer for up to 1 year in an air tight container. Thaw in the fridge.