4 cups (1 quart/litre) milk- I used organic whole milk
2 tbsp. plain yogurt (store bought to start off with)
That's it! Begin with putting the milk into a heavy pot, and bring it to a boil. Once it begins to bubble up, take it off the heat, and cool it down to 110 degrees F. I did this quickly by putting the pot into my sink that I had plugged with cold water.