Mix the milk and powdered milk in a large stockpot and slowly bring to 180 F, stirring often. Then remove from heat and let temp drop to 110F, stirring often.
Stir in 4 tablespoons plain, unpasteurized yogurt and place into containers and place in dehydrator (or oven) set at 115 F for 12 hours.
When done, keep in refrigerator or you may freeze.
Add fruit, sweetener, and/or flavorings when serving.