How to make a roux
A roux is used to thicken sauces. It's basically flour cooked in oil, stirred constantly to cook and eventually brown the flour. The longer you cook the flour, the browner it becomes to the point you can actually burn it. .
The Cajuns in Louisiana generally cook three different types of roux: blond, brown and dark brown. The darker the roux, the less stock it will absorb.
½ cup vegetable oil
¾ cup all-purpose white flour
Set a heavy 4-quart cast-iron or other heavy-bottom pot over medium heat. When hot, add oil and heat for 3 minutes. Add flour, stirring constantly with a flat-bottom wooden spatula. Stir until combined and slowly turns a light brown colour.
Continue stirring for about 15 - 20 more minutes or until roux is a chocolate brown colour. Roux has to be stirred continuously to prevent burning.
What's the difference between a roux and a béchamel sauce?
A roux is a mixture of (usually) equal quantities of flour and butter that's used as a thickening agent in sauces. A béchamel is a sauce made using a roux with the addition of (usually) milk