6 extra-large egg yolks, at room temperature*
1/4 cup sugar
1/2 cup good dark rum, divided
1 1/2 cups brewed espresso, divided
16 to 17 ounces mascarpone cheese
30 Italian ladyfingers, or savoiardi
Bittersweet chocolate, shaved or grated
Confectioners' sugar (optional)

Whisk the egg yolks and sugar in the bowl of an electric mixer fitted with the whisk attachment on high speed for about 5 minutes, or until very thick and light yellow. Lower the speed to medium and add 1/4 cup rum, 1/4 cup espresso, and the mascarpone. Whisk until smooth.
Combine the remaining 1/4 cup rum and 1 1/4 cups espresso in a shallow bowl. Dip 1 side of each ladyfinger in the espresso/rum mixture and line the bottom of a 9 by 12 by 2-inch dish. Pour half the espresso cream mixture evenly on top. Dip 1 side of the remaining ladyfingers in the espresso/rum mixture and place them in a second layer in the dish. Pour the rest of the espresso cream over the top. Smooth the top and cover with plastic wrap. Refrigerate overnight.

Before serving, sprinkle the top with shaved chocolate and dust lightly with confectioners' sugar, if desired.

*RAW EGG WARNING The American Egg Board states: "There have been warnings against consuming raw or lightly cooked eggs on the grounds that the egg may be contaminated with Salmonella, a bacteria responsible for a type of foodborne illness. Healthy people need to remember that there is a very small risk and treat eggs and other raw animal foods accordingly. Use only properly refrigerated, clean, sound-shelled, fresh, grade AA or A eggs. Avoid mixing yolks and whites with the shell?"

Note:
To make espresso for this recipe in your electric drip coffee maker, use enough water for 4 cups of coffee plus 1/3 cup of ground espresso.

You can find savoiardi and mascarpone in an Italian specialty store.