To see the process of how to thicken food using roux, just follow the photos order. 

 

1. Make sure you use the right pan.

   You will need a pan with a thick bottom to avoid the sauce sticking.

   

2. Select one of the two methods for using roux.

   If you have already prepared the roux (the case described here), place a quantity of the roux in a bowl and add a little of the warm stock, stirring to create a thick batter.

   

3. Pour the batter into the pan with the stock and continue with the next step.

   If you are making the roux that moment, add the warm liquid to the roux mixture until combined well and continue with the next step.

   

4. Stir well with a whisk and use a spoon to stir around the edges of the pan.

   

5. Simmer over very low heat for about 30 minutes.

   Stirring frequently to avoid the sauce sticking to the pan, and remove the film which forms on the surface.

   

6. Strain through a fine sieve.

   If not planning to use immediately, cool well, stirring occasionally to avoid a film forming on the surface.