Many dishes benefit from being thickened. Cornstarch slurry is popular but so is the addition of a roux, and it gives a better mouth feel. With equal parts (by weight) all purpose flour and softened butter you can make roux cubes in minutes with nothing but one pot, a wooden spoon and an ice cube tray or two.
Simply heat equal amounts of flour and butter (a pound each) over medium-low heat. Stir often until the mixture begins to darken slightly and appears a bit crumbly. Spoon equal amounts into separate ice cube mold until all are filled. NOTE: the butter will be extremely hot and can burn tender hands.
Place the molds in the freezer. The next day dump the little blocks out and store them in a ziploc bag for later use. Each block represents about two heaping tablespoons of roux.
Remember, both cornstarch and flour based thickeners are activated by heat. There are advantages to either but they are different. The roux imparts a pleasant mouthfeel and the cornstarch slurry provides sheen. For those reasons, chefs often combine the two treatments to produce a great tasting sauce with a delightful glistening appearance.
Roux blocks can be sliced or cut in any way you wish. If the liquid is hot, the buttery gens will melt right away and your dish will magically begin to thicken. Obviously, a thinner sauce takes less roux, while a thicker sauce takes a bit more. Try adding a sliver at a time and give it a few minutes to work. Keep stirring gently and you will soon see your dish tighten up before your eyes. You can always put more in but it’s difficult to take it out.