I made my own butter not long ago, I just got heavy cream (heavy whipping cream is about the same thing) and put it in my Kitchen Aid with the paddle for awhile.  it fluffed up, then went solid fast and splashed buttermilk all over because I wasn't paying attention.  But the butter was nice and soft until after refrigeration, and I put the buttermilk into some bread.  It was an intereting novelty.