Turn a small amount of commercial yogurt (or your own yogurt starter) into a large amount of custom yogurt!
2014.06.12 - First (Failed) Attempt
The yogurt was in the oven shortly before noon, and I let it 'set' for about ten hours. The results were edible but unspectacular. I heated the milk in a pot directly on the electric burner, and despite constantly stirring I still lost some protein to the bottom of the pot. The oven's minimum temperature is 135-140F, so I suspect it eventually killed the yogurt culture and prevented it from souring as much as I would have liked.
2014.06.13 - Success!
In my next attempt, I used a homemade double-boiler with much better results. I bypassed the oven's limitations by placing a temperature-controlled space heater in the oven chamber. I added a dash of vanilla to the mixture as well. The yogurt came out creamy and delicious, totally indistinguishable from store-bought!
2014.06.27 - Variations
I prepared 3/4 gallons of yogurt, this time with vanilla (2 TBsp) and coconut milk (1/8, 1/4, 1/3, and 1/2 C per 2.5 C).
I held at 180-190F for 20 minutes, chilled to 130F, mixed with yogurt culture, distributed, and incubated.