In a large sauce pan with a heavy bottom (or a double boiler) over medium-low heat warm the milk, stirring frequently, to 170-180° F.
Remove from heat and allow the milk to cool to 100-115° F.
You can place the pot in an ice bath in your sink to speed up the cooling process.
Whisk in the yogurt and transfer the mixture to a ceramic or glass container with a lid.
Wrap the container with a few kitchen towels and place it in a warm place for 8-12 hours or until thickened. An oven with the light turned on is a good option.
Stir and refrigerate the yogurt overnight or for at least 8 hours.
