Roux: Roux is flour and fat cooked together and used to thicken sauces. Roux is typically made from equal parts of flour and fat by weight. Slurry: A slurry is another method used in cooking to thicken gravy our soups. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pump.