In a large pot set over medium-low heat, gradually warm milk to 180˚, gently stirring occasionally to prevent scorching. Meanwhile, prepare a warm water bath. Fill a Dutch oven or roasting pan one-third of the way up with water and warm over medium heat to 110˚. Set aside.
Remove milk from heat and allow to cool to 110˚. Gently whisk in yogurt (or yogurt culture) until no lumps remain. Transfer mixture to 1-quart mason jars and place in warm water bath. Cover jars loosely with a clean dishcloth and let rest undisturbed until set, 5—6 hours, maintaining yogurt temperature at 110˚. Place lids on jars and transfer to refrigerator to thicken, about 12—15 hours. Stir and enjoy.
NOTE: Lynch uses yogurt to culture the milk, but pre-measured, granulated yogurt culture can be found online.