Creamy Dreamy Greek Yogurt
After it has heated for the two and a half hours, turn off the crockpot and let it all just sit on the counter for another three hours.
After that time is up, dip out two or three cups of the milk and whisk 1/2 cup Greek yogurt (from the store or from a previous batch) into it. Add this all back to the rest of the milk in the crockpot.
Line a colander with a piece of fabric. I cut up an old white T-shirt. Place the colander into a pan or bowl that will support it with enough room for the whey to drain into without touching the bottom of the colander. Cover with plastic wrap or aluminum foil, then put it in the fridge for about 6 hours. If it's thick enough for you at the end of that time, spoon it into a container and cover.
Mine seems to get too thick and I end up stirring some whey back into it. I get a little over 3 cups of yogurt plus a whole bunch of whey. If anyone has a good idea of what to do with the whey, please let me know. I hate pouring it down the sink, but rationalize that making the yogurt is sooooo much cheaper than buying it at the store that it's okay.