Whisk milk and dry milk powder together in a saucepan over medium heat until almost boiling, about 4 minutes. Cool milk to lukewarm (100 to 110 degrees F/38 to 45 degrees C).
Gently stir kefir into milk mixture until just blended. Pour mixture into yogurt containers or slow cooker. Cook on Low
Cook on Low until desired level of tartness and yogurt consistency is reached, 4 to 10 hours. Chill yogurt in the refrigerator, at least 2 hours.
