Heat 2 quarts milk in a saucepan over medium heat until a candy thermometer inserted in the liquid reads between 180 and 190 degrees F (82 to 88 degrees C), 8 to 12 minutes. Remove from heat.
Whisk powdered milk and honey into the warm milk. Let cool until the thermometer reads between 115 and 120 degrees F (46 to 49 degrees C), about 1 hour and 15 minutes.
Whisk a small portion of the warm milk mixture into the yogurt; stir mixture back into the saucepan. Transfer mixture into a warm slow cooker. Wrap slow cooker in a bath towel and tuck it away into a microwave or oven. Let sit until thickened into yogurt, 6 to 9 hours.
Line a colander with cheesecloth or coffee filters and set over a bowl. Pour the yogurt into the colander and refrigerate colander and bowl until desired consistency is reached, 4 to 8 hours.
