1 pint heavy cream
2 tablespoons cultured buttermilk

Pour the cream into large mixing bowl and add the buttermilk.
Stir until well-mixed but do not whip the cream.
Let the cream and buttermilk sit covered on the counter for 24 hours.
After 24 hours, stir the cream and transfer to a storage container such as a Mason jar or Tupperware.
Store in the refrigerator for up to 10 days.