Put milk in large saucepan and heat it over medium heat till boiling. Put the milk aside and let cool for about 35-45 min. You can check the milk with small finger -- it (the milk) should be warm, but not very hot (If you wish you can use thermometer: 43-45 C).
Beat yogurt with fork or steel whisk in a bowl. Add 1 cup warm milk, mix well. Little by little add yogurt-milk mixture to the rest of the milk. Mix again. Pour milk into glass jars or ceramic bowls with lids. Put jars on a flat surface. Cover with something that will keep it warm, as a folded blanket or a sleeping bag (I am using a sleeping bag). Let it stay for 2 hours and 30 min. Check "kiselo mlyako" - it should be thick. Let stay uncovered at room temperature for 30 min. Put in the refrigerator for 3-4 hours.
Enjoy the results. Makes 8 lb. Do not forget to save 1 lb. to make next portion of "kiselo mlyako".