Bring whole milk - however much yogurt you want to make - up to just below a boil (180 degrees) in a heavy bottomed pot
Take off heat and allow to cool to 110 degrees.
Stir in 1 T full fat, live culture yogurt per 1 quart milk - can use previously made homemade yogurt, or even better yogurt whey, for this
Place in clean vessels and allow to rest in warm place (microwave with stovetop light on) 8-10 hours or until firm and desired tang achieved.
NOTE:
This exact same procedure, made with 1 spoonful whey + 1 c heavy cream, yields creme fraiche!
Can be used as sour cream in anything that might curdle, this stuff won't break!
Or on fruit, or biscuits, or anything!
ANOTHER NOTE:
If you make butter from creme fraiche, you get cultured butter!!