Remove pot from the heat and place it in an ice bath. Let the milk cool until lukewarm (115 degrees).
Stir in the yogurt starter or yogurt, mixing well. Pour mixture into a quart jar.
Set the jar in a warm spot for 8 to 10 hours, or overnight, to culture and set (time depends on desired firmness). Set in your oven with just the oven light on.
After the yogurt is set, place yogurt in refrigerator for at least 45 minutes before eating. Flavor and top as desired.