In a clean jar, fill half way through with the whipping cream.
If you're using a blender or food processor, pour the cream into the food processor jar and pulse.
Or in a blender cup
Continue until you have the consistency below, number 8 and 9.
The cream is changing about to start curdling.
Continue to shake and you will notice the cream has started to thickens, you can open to check what going on.
Rinse the butter with cold water (add the water with the rest of the buttermilk)