This is an extension of my previous post on bread... which I guess I need to repost because I think it was on a previous iteration of the forums. So I was messing around with my bread recipe and making butter at the same time. Not that shit you make in kindergarten where you shake the jar full of cheap cream, but nice, quality, cultured butter. I put a jar of good heavy cream in a yogurt maker along with jars of milk, mix in some lactobacillus and basically come out with a substance similar to creme fraiche. Then, I whip the creme fraiche until it turns to butter and salt it. The lactobacillus does something special there that's hard to describe, but its not longer butter but something magical (especially if you add in some roasted garlic and a touch of honey). Anyway, the real point is that afterward, you are left with real, cultured buttermilk as well.
So later on, I was making the preferment for the bread (I use a poolish) and I had all this buttermilk left. I thought, "Hey, what if I replaced the water in the poolish with the cultured buttermilk? It's got all those live lactobacilli cultures in it, so it should basically work out like a sourdough starter (I know it's not going to be wild yeast this way, but that's the whole point)". I left it out a bit longer than I would normally do it and let it sit on the counter overnight and then moved it to the fridge for another 24 hours because I didn't have time to make any bread that day. In the meantime, it got super bubbly and a sour/sweet smell (kinda like mead).
I used the rest of my standard recipe to make the bread and was left with a nice bread with great yeasty flavor and tangy sour notes (not like a full-on sourdough though). I'm assuming that instead of using fresh, cultured buttermilk that I could have used active yogurt and water and gotten close to the same result. But the result combined with the cultured butter on top is so simple but so good.