Bring the milk to 190F
Let the milk cool to 115F gently , stirring every 30 minutes.
In a separate bowl, gently whisk 2 cups of milk with 1 cup of active yogurt or cultures.
Gently pour the mixture back into the crock pot, and gently stir everything together.
Place the covered crock pot in a warm area for 8-24 hours. Oven with the light on seems to be perfect. I like 14 hours; longer time makes the yogurt more tangy.
Line a colander with cheesecloth.
Slowly transfer 1/3 of the yogurt to the colander, and let drain for 1-2 hours, depending on how thick you want the yogurt.
Save 1 cup of yogurt in an airtight container in the fridge - use within 4 weeks.