I spent a few months working in a restaurant that used a ton of house-made crème fraiche. A single batch would be made in a 22-quart Cambro container, where you add 16 quarts of heavy cream and 2 quarts of buttermilk and let it sit out for a few days covered with cheesecloth before transferring it to quart containers and storing it in the fridge. That’s way more crème fraiche than what we need at home, but I loved the utter simplicity of the 8:1 heavy cream to buttermilk ratio. The way that the liquids combine together and sit at room temperature to create this completely different flavor and texture is truly magical. When making a slightly smaller quantity at home, I found that it would thicken up after a day or two, instead of the three days we would traditionally wait at the restaurant. Note that it helps to find yourself some good-quality cultured buttermilk before you try to make this.