In this recipe hot sugar syrup is mixed into the egg yolks.

In a small saucepan, combine the sugar and water and bring to a boil, stirring, over medium heat. Continue to boil, brushing down the sides of the pan with a brush dipped in cold water, until it reaches the soft- ball stage, or a candy thermometer registers 240 deg.F.

In a bowl, using an electric mixer, beat the yolks until they are combined, then add the sugar syrup in a stream. Beat until cool. Beat in the vanilla.

In a bowl, whisk the mascarpone and rum until smooth. In another bowl, beat the heavy cream until it holds soft peaks. Combine the egg mixture with the mascarpone. Fold in the heavy cream.

Line a 6-cup serving dish with the biscotti and drizzle the espresso over them. Spoon in the mascarpone mixture, smoothing the top, and chill, covered with plastic wrap, for at least 3 hours or overnight. Before serving, sprinkle the top with the grated chocolate.