Italian for "half cold," semifreddo refers to the consistency of the dessert in these cups: The mixture is frozen, but not as hard as ice cream.
Whisk 1 cup cream until stiff. Set aside.
Fill a large bowl with ice and water; set aside. Place a large metal bowl, or the top of a double boiler, over a medium saucepan of barely simmering water. In it, whisk together egg yolks and 2 tablespoons sugar until pale yellow. Whisk in Cognac and espresso powder. Gradually whisk in Marsala. Whisk vigorously until mixture becomes thick and glossy, 2 to 3 minutes. Remove from heat; whisk mixture over the ice bath until cool. Set aside.
In the detached bowl of an electric mixer, whisk together egg whites and remaining 4 tablespoons sugar. Place over a saucepan of barely simmering water; continue whisking until sugar is dissolved and mixture is hot to the touch, about 2 minutes. Replace bowl on mixer stand, and beat mixture until stiff and glossy.
Fold a third of the whipped egg whites into egg-yolk mixture. Repeat with remaining egg whites, a third at a time. Gently fold in reserved whipped cream. Spoon mixture into 6 cappuccino mugs, cover, and place in freezer until frozen, about 1 1/2 hours.
Whip remaining 1/2 cup cream. Spoon over frozen semifreddo. Garnish with chopped torrone or almonds, and serve immediately.