1 cup Amaretto cookies, crushed, plus more whole for garnish
Fill a large saucepan with about 2 inches of water; bring to a boil over medium high heat. As soon as the water boils, reduce the heat to low or medium low to maintain a low simmer.
Whisk together the egg yolks and sugar in a heatproof bowl and set it down over the pot of simmering water. Make sure the bottom of the bowl does not touch the water. Whisk vigorously or use an electric mixer. When the mixture is foamy, add the Marsala and continue beating until the mixture doubles in volume and becomes a dense, foamy cream.
Remove the bowl for the heat and let cool. In the bowl of a stand mixer, whip the cream until it reaches the stiff peak stage. Fold into the cooled egg mixture.
Butter and spray six ramekins and add about a tablespoon of crushed cookies to the bottom. Pour in the whipped cream and egg mixture to the top of each ramekin and top with more crushed cookies. Cover and place in the freezer for at least 6 hours.
When ready to serve, remove the desserts from the freezer and let them stand at room temperature for at least half an hour. To further help in releasing the semifreddo onto your dessert plates, put the ramekins in a hot water bath briefly and run a paring knife around the edges. Invert your dessert plate onto the ramekin, then give a firm shake. You should hear the semifreddo release.