I looked up a ton of yogurt recipes before I tried this and they were all more or less the same. 8-ish cups milk, 1/2-ish cup yogurt starter, maybe 1/3 cup powdered milk (I did not use this), temp goes up, then down, then stays the same for 3 to 18 hours. Here is what I did and Grace and I ate a bunch and no one has a tummy ache.
I put a quart of milk in a pan and brought the temp up to 180 degrees over low heat. (I kept a thermometer in the whole time). Then I turned the heat off and let it cool to 110 degrees and stirred in 1/2 cup Nancy's yogurt, because it is the best kind. I was baking bread and cobbler and cookies this day so I just left the pot on the stove where it was warm all day long. If the temp went down to like 95 degrees or so I turned the heat back on low for a second. I just tried to keep the temp between 95 and 110. About 8 or 10 hours into this process a big layer of whey formed at the top. I get a little thrill any time whey separates, so this was fun. Some of the recipes mentioned this and some did not. The ones that did said to either pour it off, mix it in, or soak it up with paper towels. I like thick yogurt so I didn't want to mix it in. But I was feeling lazy, so I poured into some muslin and let it hang for about 20 minutes. The yogurt is thick and creamy and mild. Easy-peasy. You just have to hang out all day. We put honey and cinnamon on it and Grace said it was "scrumptious." Also I saved the whey and made pancakes with it.
And just in case you want it: Whey Pancakes (KAF!)
2 cups flour (white or whole wheat)
1-2 Tablespoons sugar, honey, or syrup
1 tsp baking soda
1/2 tsp salt
2 cups whey
2-4 Tablespoons oil
Mix dry stuff together. Mix wet stuff together. Mix those together until JUST combined. And cook 'em up. If ya'll have a sourdough pancake recipe I will die of delight. I love pancakes, but I LOVE sourdough pancakes.