Add the heavy whipping cream to the bowl of your mixer.
Start to whip the cream. You will while the cream past the point of making whipped cream. As you continue to whip the cream, it will begin to separate, and you will start to see the liquid buttermilk fall out.
You will continue to whip the cream until you lump bright yellow butter surrounded by the liquid buttermilk. This could take up to 10 minutes.
Strain off and reserve the buttermilk.
Store in an airtight container until you are ready to use it.