first, start by making crème fraîche:
1 quart heavy cream
2 tablespoons either buttermilk or live, active, plain yogurt (homemade or store-bought)
note: I use my homemade yogurt, and it works perfectly, though the buttermilk method also works quite well. if you start making your own butter, you'll end up with your own cultured buttermilk as well! my yogurt, crème fraîche, buttermilk (and to a lesser extent, the butter) all contain the same culture.
sterilize your equipment: thermometer, pot in which you're heating the cream, whisk/or spoon used to add the culture (buttermilk or yogurt). most of the recipes I've read instruct to warm the cream to 110 F first, then to innoculate with culture (whisk in the buttermilk or yogurt) and allow to stand, covered, in a warm spot for 8-12 or more hours. ***yet another "do as I say, not as I do:" I've found that when using UHT (ultra-high temperature) pasteurized cream (which is ALL I can find around here), I don't have to bother with heating the cream at all to start it, so I skip this step.*** I like using my heavy Le Creuset dutch oven for this, even if I'm not heating the cream. my gas oven, which has a pilot light that's constantly on, keeps whatever I'm culturing right at the perfect temperature (about 110 F), and when I use store-bought yogurt, or my homemade yogurt or buttermilk to culture it, it's always nice and thick (like sour cream) and perfectly tangy at 8-10 hours (it seems to take a few hours longer when I've used commercial buttermilk). if I want it more liquid and only slightly tangy, I make sure to check it at 6 hours. any way you like it, culture to your taste, then pack into sterile containers (I use glass canning jars) and refrigerate. it keeps for about a week.
the above recipe makes a LOT of crème fraîche; more than I'd ever use in a week! it's easy to make a half recipe or even a quarter the volume; I make a whole quart so that I can take about 3/4 of it and make my own cultured butter:
3 cups of chilled crème fraîche
salt to taste, if desired
get your equipment set up before you start whipping the cream. you'll need either a food processor or electric beaters and a bowl, a quart or more of ice water in a pitcher, a large clean jug or measuring cup (one that holds 1 quart or more) into which you'll strain the buttermilk, a medium-large fine strainer/sieve and a large bowl in which you'll clean the butter (using the ice water). if you want to add salt to the butter, you'll also need a clean cutting board to knead it in.
I use my food processor to make butter, fitted with the "s" blade. put all of the crème fraîche into the food processor bowl and process for several minutes OR put all of the crème fraîche into a bowl and start beating it with your electric beaters. whichever method you use, be sure to listen to the sound of the cream being beaten. there will be a significant change when it breaks down into butter and buttermilk, and the buttermilk will start to splash around. at that point you will see clumps of pale yellow butter floating in white buttermilk. stop processing, place the strainer over the jug (or large measuring cup) and pour the mixture in. the strainer will catch the butter, and the buttermilk will flow into the jug. pour the buttermilk into a clean jar (3 cups of crème fraîche will yield about a pint of buttermilk) and use in pancakes, waffles, or any other recipe for which you'd use regular buttermilk. you can also freeze it for later use. keep the strainer over the jug and pick up the butter, squeezing out as much liquid as possible, then place it into a bowl and pour ice water over it. knead the butter in the ice water for a few minutes, then pour off the water. add more ice water and knead again; continue pouring off, adding fresh ice water and kneading until the liquid you pour off is clear. at that point, the butter has been cleaned of all buttermilk and will keep well. if you want to add salt to it, you can knead in a small amount (to taste) on a cutting board. shape the butter however you'd like: you can press it into ramekins, or form it into sticks or logs. cover ramekins with plastic wrap, and wrap sticks or logs first in wax paper, then in foil or plastic wrap. I usually keep one stick in the fridge to use and freeze the others until I need them. use the butter as is, bake with it; whatever you'd like. it's heavenly.
I have found that I like to use crème fraîche on my toast instead of my usual butter, especially on good, crusty sourdough bread. the rich, tangy taste is just a tiny bit better on toast than my gorgeous homemade butter, and I figure over time, maybe I'm saving my body from having to deal with a few more grams of fat (not much, but what the heck). the cultured butter I make is even better than cultured butter I've bought at the store (and of course it costs much less to make it at home), and it's also excellent on toast, so if you prefer, make *all* of your crème fraîche into butter.
now I need to find or develop a truly excellent recipe for buttermilk bread, so I can use mine up! the buttermilk that results from making cultured butter is delicious; slightly tangy and very refreshing. I can actually understand why people drink buttermilk now! I usually drink a small glass of it each time I make butter. enjoy!