Step 1

Heat milk in a large saucepan over medium-high heat, stirring frequently, until it is steaming, barely bubbling and registers 180 degrees F on an instant-read or candy thermometer. (Do not leave unattended--it can boil over very quickly.)

Step 2

Carefully pour the milk into a clean, heat-safe 5- to 8-cup container. Let stand, stirring frequently, until cooled to 110 degrees F. Combine yogurt with 1/2 cup of the 110 degrees milk in a small bowl, then stir the mixture back into the warm milk.

Step 3

Cover the container and wrap in a clean kitchen towel to help keep it warm. Place in a very warm place (see Tip) and let stand, undisturbed, until thickened and tangy, at least 8 hours and up to 12 hours. Refrigerate until cold, about 2 hours. The yogurt will thicken a bit more in the refrigerator.

Step 4

Line a large fine-mesh sieve with 2 layers of cheesecloth and place over a large bowl. Spoon the cooled yogurt into the cheesecloth, cover and refrigerate for 8 to 24 hours, depending on how thick you want it.