Shall we try making butter?

Call it French butter, or call it cultured butter; we begin with heavy cream, doctored with either plain yogurt or buttermilk, and we allow it to sit at a warm room temperature for twelve to eighteen hours. Start in the mid-afternoon, so that by the next morning, the kitchen gods willing, you may churn it up and wash it (no kidding -- you wash butter by mashing it repeatedly with ice water and pouring off the watery residue each time), and share it with a friend. Along with a loaf of that delicious challah. 

I'll let you know.