One of the fun things about working on the book is the “need” to test everything. I say “need” because, in truth, it’s a lot of fun to geek out over the details and try more permutations than I might otherwise try. (Just like a good coder, gotta try to hit the boundary conditions in writing recipes!)
Yogurt is really way easier to make than I thought: toss a spoon of yogurt into a container of milk and let it sit long enough in a warm environment, and the bacteria from the yogurt (needs to be “live culture”) will chow down on the lactose in the milk. My oven hovers around 110 F when the oven light is on (it probably helps that it’s 9 billion degrees outside right now) – easier than pie.
There are some precautions you should take to avoid culturing the wrong kind of bacteria, so if you want to be thorough, you should do a bit more than “just” toss milk+yogurt into the oven. For a good write-up, see extension.missouri.edu/publications/DisplayPub.aspx?P=GH1183.