Adapted from a recipe by Kenji Lopez-Alt at Serious Eats. http://bit.ly/cuRxay - Despite the presence of whipped cream, this is real ice cream, not frozen mousse! The trick is to freeze the base as quickly as possible, using ice cube trays. Then, blend the frozen custard cubes with more cream until smooth. This prevents too many ice crystals from forming, and limits the amount of overrun.