Mascarpone Semifreddo with Raspberry Sauce Recipe

In a food processor or blender puree the thawed raspberries and working over a saucepan force the puree through a fine sieve to remove the seeds. Bring the puree to a simmer, stir the cornstarch mixture, and add it and the lemon juice to the pan. Boil the raspberry sauce, stirring, for 1 minute, let it cool and chill it, covered. The sauce may
be made 2 days in advance and kept covered and chilled.
Line a metal loaf pan, 9x5x3 inches, with plastic wrap, leaving a 2 inch over-hang on the ends, and chill it in the freezer.
In the bowl of an electric mixer beat together the yolks and the sugar until the mixture is thick and pale and beat in the mascarpone, the vanilla, and the zest.
In a bowl, beat the egg whites until they just hold stiff peaks and fold them into the yolk mixture gently but thoroughly. Spoon half the mascarpone mixture into the chilled pan, sprinkle it with the chocolate, and spoon the remaining mascarpone mixture onto the chocolate, smoothing it carefully.
Freeze the mixture, covered with plastic wrap, for 8 hours or overnight and unmold the semifreddo onto a serving dish. Arrange the fresh raspberries decoratively on the top and serve sliced with the raspberry sauce.