serveitforth.com recipes
Crème Fraîche
1 part buttermilk
8 parts heavy cream
(For example, 1/4 c of buttermilk for 2 c of heavy cream)
In a clean glass jar or clean, odor-free plastic container, combine the buttermilk and the cream. Cover loosely (it should be protected from dust, etc, but have a little room to breath) and put in a draft-free place. Give it a stir after several hours and, if it's not thick, give it more time. It will take anywhere from 12 to 24 hours for the cultures to work their magic. The warmer your kitchen, the quicker the process. When it has thickened, put a tight lid on it and store it in the fridge where it will keep for 1 to 2 weeks.
To make the next batch, substitute some of the existing crème fraîche for the buttermilk.