How did you make homemade creme fraiche?

Been making it for decades now! Always have some in the fridge. My formula is 2 Tablespoons of (real) buttermilk to 1 cup heavy cream. [Real buttermilk is sold in health food stores or dairies and farm markets. It's not the stuff in cartons in the supermarket.] Sometimes I refresh my creme fraiche by adding more heavy cream to the creme fraiche jar. (kinda like replenishing sour dough.)

You can also culture it with kefir. The temperature in your home will dictate how long it takes.
If you use raw cream, it will actually culture itself. Just seal it in a jar on the counter and wait about 24 hours. Amazing stuff!

My recipe is one I can always remember: 1 cup heavy cream (not ultra pasteurized though) + 1 T. buttermilk, usually doubled. Mix in a glass or ceramic bowl. Cover and let sit for up to 24 hours. I always have some on hand and use it like sour cream, heavy cream, whipped cream or even ricotta.

Here is how I make it. I make a batch at least once a week because it is quite wonderful to have on hand as a staple for vinaigrettes, or mixed with a bit of good honey to top a dessert, or in place of cream (plus some baking soda) in scones or biscuits, in ice cream.......http://wp.me/p27pPl-il

This needs to sit for 8-24 hours at room temperature, not in the refrigerator.
In a glass or ceramic bowl (not metal), whip together 1 cup h¬eavy cream and 2 tablespoons of either buttermilk or regul¬ar sour cream (not low fat). It would be fine to use a glass jar with a screw top, otherwise cover bowl with plastic wrap. After that period, refrigerate – keeps for about a week.