A roux is used to thicken all kinds of dishes, especially soups. Usually corn flour is used to thicken soups and other dishes, like chicken Manchurian, sweet and sour chicken, beef chilli etc. Roux thickens the soup through gelatinization, a process in which starch granules absorb the liquid and expand several times their original size. Like corn flour, roux also has several applications, but mostly it is used to give desired consistency to soups.
Unsalted butter, rendered bacon fat or canola oil - 1 cup
All-purpose white flour - 1¾ cups
Take one cup of unsalted butter (or any other fat of your choice) in a sauce pan and heat it on medium flame for 3 to 5 minutes.
Once the butter starts simmering, add 1 ¾ cups of all purpose floor and mix it well using a whisk. Cook the roux for several minutes, until it gets the colour appropriate for your soup. Keep stirring the roux as it cooks to prevent it from scorching and uneven cooking.
Colour and cooking time of roux varies for different soups, e.g. if you are making cream-based vegetable soups, like cream of mushroom or cream of tomato, use white roux cooked for 3 to 5 minutes. For dark coloured soups, such as beef, use brown roux cooked for 35 minutes.
Once done, store the roux in an airtight jar and place it in the refrigerator.
Add roux to your soup and allow it to simmer for 15 to 20 minutes, or until the soup attains the desired consistency and a smooth texture. Taste your soup before removing it from the stove, if the starch granules are sticking to the back of your tongue, cook it a little more.