In a medium bowl, whisk the egg yolks and sugar until blended. Whisk in 1/2 cup cream, the marsala and salt. Place the bowl over a large saucepan of simmering water (do not let the bottom of the bowl touch the water). Whisk constantly until the mixture is thick and a thermometer inserted into the center registers 160 to 170 degrees F, about 15 minutes. Place the bowl on a work surface and add the chocolate chips. Whisk until the chocolate chips are melted and the mixture is smooth. (Can be made 1 hour in advance. Let stand at room temperature. Whisk before using.)
Whisk the remaining 1/3 cup cream and the mascarpone in another medium bowl until thick. Dice the cake into small cubes. Place about 1/2 cup of the cake cubes into each of 6 old-fashioned glasses or water goblets. Spoon 2 heaping tablespoons of zabaglione on top. Top with a dollop of the mascarpone mixture. Repeat the layers. (Wrap any leftover cake cubes in plastic wrap and freeze.) Top with white chocolate curls and serve.
Recipe courtesy of Giada De Laurentiis