1 A roux is usually a mixture of equal weights of butter and flour, and is used to thicken sauces and stocks. I like to use a little more flour, but this is personal choice.
2 Melt the unsalted butter in a solid/heavy based saucepan, when it has just melted take the pan off the heat and add the flour at one go. Stir with a wooden spoon until the mixture is smooth and has left the sides of the pan.
3 Return to the heat and cook as follows: for a Roux Blanc/Blond cook for a few minutes only, stirring all the time until the mix is just starting to colour, use this as a base for white sauces such as crème and béchamel.
4 For a Roux Brun cook for a little longer until it is light brown in colour, use this for darker sauces and gravies.
If you are going to use roux on a regular basis make a batch up and keep in an airtight container in the refrigerator.