Heat the milk. Pour the milk into a Dutch oven and place over medium to medium-high heat. Warm the milk to right below boiling, about 180-190°F. Stir the milk gently as it heats to make sure the bottom doesn't scorch and the milk doesn't boil over.

Cool the milk. Let the milk cool until it is just warm to the touch, 112°F to 115°F. Stir occasionally to prevent a skin from forming.

Thin the yogurt with milk. Scoop out about a cup of warm milk into a bowl. Add the yogurt and whisk until smooth and the yogurt is dissolved in the milk.

Whisk the thinned yogurt into the milk. While whisking gently, pour the thinned yogurt into the warm milk. This inoculates the milk with the yogurt culture.

Transfer the pot to the (turned-off) oven. Cover the Dutch oven and place the whole pot in a turned-off oven, wrap the pot in towels to keep the milk warm as it sets. Leave it undisturbed for 10 to 12 hours, for a thicker, tangier yogurt, let yogurt sit an additional 3 to 5 hours.

Transfer the to storage containers, cover, and refrigerate.