So I've done it twice now. It was taking 15-20 minutes in the Kitchenaid for the cream to break. In the food processor it takes less than a minute (2 cups of cream, cold from the fridge) using the regular cutting blade, which is all I have. I quickly pour out the buttermilk and replace it with cold water, and run it for another 10-15 seconds or so. Then I transfer the butter to a bowl for the rinsing / kneading part.