Kashk is a very interesting thick, creamy paste made out of yogurt, which tends to have a cheesy flavor and a color that may be yellowish to greyish. The paste is used in cooking, pretty much as crème fraiche, parmesan, or sour cream would be used, for enhancing the flavor of the recipe. In Persian cuisine, from where kashk comes, it is used in soups, as a dip, in stews, with eggs, or in various other recipes. So, now you may see that this is not the typical kind of yogurt available anywhere. In fact, it takes a bit of knowledge and patience to make kashk, but if you are willing to try it, here is what you need to know.
You will need plain yogurt, whole-fat would be ideal as it will give your kashk the creamy consistency that made it famous. The yogurt will have to the soured by leaving it at room temperature, for 1 or 2 days, until it acquires a sour taste. Then you will have to mix the soured yogurt with an equal part of water and placed on the stove, where you will simmer it for several hours until the liquid evaporates. This process may take up to 4 hours, as you will have to obtain a thick but loose pulp, as the yogurt is breaking down. The obtained pulp will have to be strained even more, by using a cheesecloth or muslin. Hang it over a bowl, squeeze it, or place weights on top of it, do as you like it as long as you get the pulp as dry as possible. Once the pulp is well-drained, you will have to place it in a blender and mix it with salt and a bit of fresh water. The idea is to obtain a creamy paste that you can use with ease when cooking. The resulted kashk can be stored in the refrigerator for a few days or even frozen, in case you prepared a larger quantity and you don’t want to consume it right away.