Heat the milk in a large pot over medium heat until it reaches 180°F (82°C).

Set aside about 1 cup of the hot milk and a spoonful of yogurt, and let both come down to room temperature.

Place the pot in an ice bath and cool the milk to about 120°F (49°C), or until you can dip your finger in comfortably.

Mix the yogurt with the reserved milk, then pour it into the pot and stir to combine.

Cover with a lid, wrap in towels or blankets, and let sit in a warm spot for 8–24 hours (longer = thicker yogurt).

Transfer to the fridge to chill for at least 6 hours or overnight. Save a spoonful for your next batch so you can make an infinite amount of yogurt.