In a large pot, slowly heat milk over med heat to 185 degrees, stirring occasionally. Milk will appear frothy. Do not overheat. You can use a candy thermometer to monitor temperature.

While milk is warming, fill a sink with cold water.

When milk has reached 185, remove from heat, cover with a lid, leaving lid cracked for steam to escape, and place pot into the water bath. Be careful not to get water into the pot.

When milk has cooled to about 100 degrees, remove a cup of the warmed milk and mix it a bowl with the greek yogurt.

Pour milk/yogurt mixture into the pot with warmed milk and stir thoroughly.

Cover the pot, wrap in a heavy towel, and place in the oven. The oven should not be hot nor turned on. Turn on the oven light and allow the milk to culture for 14-18 hours.

Once yogurt has set, you can drain the yogurt through cheesecloth for an even thicker preparation or simply strain off whey (yellow liquid) and refrigerate immediately. Store yogurt in glass containers.