1 qt whole milk (my preference is whole, but you could probably use whatever kind you have)
2 Tbsp. plain yogurt
Candy thermometer (with range from 115 - 180)
Glass quart jar with lid (like a canning jar, or you could use 2 smaller jars)
Huge soup pot
Pyrex glass measuring cup
2 qt (ish) saucepan
1. Measure milk and pour into a medium saucepan. Start it heating up over medium heat. Rig your candy thermometer so its tip is in the middle of the milk. I do this by sort of threading it through the wires of a wire whisk. Stir occasionally with said whisk.
2. In your now-empty pyrex measuring cup, measure out 2 Tbsp. yogurt to start hanging out at room temperature.
3. When your milk gets to 180 degrees, remove from heat. Let it cool down to 115 degrees. This takes a while...but exactly how long depends on how warm your kitchen is, among other things.
4. Pour a little cooled milk (115) into the Pyrex holding the (now room-temp) yogurt. Using that same old whisk, whisk it together real good. Then pour the yogurt-milk mixture back into the saucepan holding the rest of the cooled milk. Whisk it all together real good, again, some more.
5. Pour into glass jar, set jar on top of heating pad set to low, cover with kitchen towel and then put huge giant soup pot on top. Leave it for 8 hours (or a little more is fine too). Then put it in your fridge and call it a day. It keeps for about 5 days.
Note: For you working women, you could feasibly start this yogurt when you get up in the AM and have it be done when you come home. But I would try it the first time on a Saturday so you'll have an idea of how much time it takes at the beginning.
Another note: You can "chain" the yogurt once you make some. When you get down to your last 2 tablespoons (or almost) you will want to make some more. You can also freeze it in 2 Tbsp. amounts; it will just require a little more forethought with thawing and all that.
Suggestion: If you want to substitute this yogurt in a recipe that calls for sour cream, you should make it into "yogurt cheese" first, by straining it for a while in your fridge. The name is kind of misleading, it isn't really like cheese. It becomes a very similar consistency to sour cream.
Final note: If you don't have a big enough soup pot to keep your yogurt incubating on the heating pad, you can try putting your heating pad on an oven rack, the yogurt on top and then just a towel snugly around it. There are different creative ways you can incubate it. It just has to stay warm for 8 (ish) hours.