Crockpot Yogurt--8 cups (half-gallon) of whole milk--pasteurized and homogenized is fine, but do NOT use ultra-pasteurized. (Debbie recommends starting with whole milk until you get the hang of yogurt-making)
--1/2 cup store-bought natural, live/active culture plain yogurt (you need to have a starter. Once you have made your own, you can use that as a starter)
--thick bath towel
Plug in your crockpot and turn to low. Add an entire half gallon of milk. Cover and cook on low for 2 1/2 hours.
Unplug your crockpot. Leave the cover on, and let it sit for 3 hours.
When 3 hours have passed, scoop out 2 cups of the warmish milk and put it in a bowl. Whisk in 1/2 cup of store-bought live/active culture yogurt. Then dump the bowl contents back into the crockpot. Stir to combine.
Put the lid back on your crockpot. Keep it unplugged, and wrap a heavy bath towel all the way around the crock for insulation.
Go to bed, or let it sit for 8 hours.