Use the best, freshest heavy cream you can find for the whipped cream. Get Ahead: This cake keeps, well wrapped, in the refrigerator for up to 4 days, and freezes fine. You'll lose the distinction of the crackly top layer against the fudgier insides, but it will still be delicious. Bring fully to room temperature before dusting with cocoa or confectioners' sugar and serving with whipped cream or creme fraiche. The whipped cream can be made up to 1 day in advance.