Use an earthenware bowl if you have one. It retains heat well. Mix the milk and yogurt in bowl. Fasten a cooking thermometer to side of bowl or float a dairy thermometer on the surface. Set bowl in oven and heat slowly to 120F. Turn off oven, cover milk to hold in heat and let cool gradually to 90F. Maintain temperature between 90F and 105F by reheating oven if needed (about two to three hours) until milk becomes the consistency of Junket. Check frequently during last 30 minutes. Chill immediately after milk thickens.
