With electric beaters, whip 50g sugar and 4 yolks till light and airy.
Whip 50g sugar and 3/4 cup heavy cream to soft peaks. Add 8oz mascarpone and whip to medium peaks.
Fold mascarpone mixture into yolks.
Make 2 cups of coffee/espresso and add rum.
For the assembly, dust bottom of pan with cocoa powder. Make a layer of coffee-soaked ladyfingers and then a layer of cream, twice. Dust with cocoa and top with shaved chocolate. Chill covered for a day.
