Combine the cream and buttermilk in a measuring pitcher and stir until you get a thick yogurt consistency. Transfer to a jar, cover with cheesecloth or muslin, and secure with a rubber band. Leave at room temperature for 12 hours.
The crème fraîche is now ready to use. If you want to drain off some liquid so it is thicker, spoon it into a sieve lined with a coffee filter placed over a bowl, and put the setup in the fridge for a few hours. Add the pepper to the cream just before serving.
