Chef John’s Crème FraÃche
The taste and texture of homemade creme fraiche are far superior to those of store-bought sour cream and are simple to make with only two ingredients.
Combine cream and buttermilk in a glass jar.
Cover tightly with cheesecloth (or any breathable material) and let sit at room temperature (70 to 75 degrees F (21 to 24 degrees C)) until thickened about 24 hours.