You need:
Large cooking pot
Food thermometer
2 tablespoons prepared Greek yogurt with active cultures
Glass bowl or crock with lid (lots of people use slow-cooker crock)
cooling rack
strainer
cheesecloth (or, if you are like me, good paper towel instead)
Large bowl
Make sure all containers, pots, utensils are super clean
| Yogurt with the marks of the cheesecloth (paper towel!) left on it | 
1/2 gallon milk (buy good milk--use skim, 2% or whole--I used 2%)
2 tablespoons plain Greek yogurt
1. Pour milk into cooking pot and place over medium heat. Measure 2 tablespoons of the milk into a small bowl. Mix those 2 tablespoons milk with 2 tablespoons Greek yogurt. Set aside.
2. Let milk come to 180°F (use candy thermometer or instant read), stirring often as temperature rises to keep milk from sticking to pot.
3. When milk reaches 180°F, pour into glass container and set container on cooling rack. Let temperature fall to 110°F.
4. Turn oven on to 150°F or Warm setting.
5. Stir up the reserved milk/yogurt mixture and add to milk in glass container. Stir to combine well.
6. Place lid on container (I used a bowl and covered the bowl with a plate). Wrap container in large dishtowel (use 2 if you have to--you want to have it completely covered, top and bottom) and place wrapped container into 150° oven. Turn oven OFF and turn oven light ON. Make sure it stays on until you remove yogurt from oven.
7. Set timer for 7 hours. At the seven hour mark, remove container, unwrap. You will have regular yogurt at this point. Place container in fridge for at least 1 hour to cool.
8. Place cheesecloth-lined strainer over large bowl. Gently scrape/pour yogurt into lined strainer. Return this to fridge and let sit about1 to 2 hours. Check yogurt after 1 hour--you can decide how thickened you want the yogurt (mine sat 2 hours in the strainer)...To store, place in sealed container and store up to 1 week. (After straining, I had about 5 cups yogurt)...
Note--I think I can make a second batch using 2 tablespoons of THIS batch--will update here when I've checked that out. My goal is to not buy ANY Greek yogurt any longer, not even as starter.
