Heat the milk to 180°F (82°C) to denature the proteins so the yogurt sets thick.

Cool it back down to 110°F (43°C).

Stir in the active yogurt starter.

Pour into a clean jar. Keep it warm - wrapped in a towel, in a slightly warm oven, or an insulated cooler - for 8 to 12 hours.

Refrigerate once set.