How to cook
Boil the milk and let it cool down to 110°F (43 °C). In an 3 1/3 cups (800 ml) jar, put 1 level tsp leaven and good yogurt. Most yogurts that are sold in stores are not suitable for this purpose.
If it is store-bought, add 1 tablespoon jars are closed with caps and wrapped in something quite a bit warmer.
Importantly, the milk is very warm. Leave it for a few hours, then move to the refrigerator.