Put six 6- ounce serving cups in the refrigerator to chill

Prepare an ice-water bath in a large pan or bowl and reserve.

Put a small bowl and the beaters of the electric mixer into the freezer to chill while preparing the egg mixture.

In a small dish, add the espresso powder to the hot coffee or hot water. Stir to dissolve then refrigerate to cool.

In a medium-size heat-proof bowl, whisk the egg yolks, 1/2 cup of the sugar, vanilla, and salt together until smooth. Set the bowl over a deep saucepan of simmering water and attach a candy thermometer to the bowl. Be sure the bottom of the bowl does not touch the water as it will begin scrambling the eggs. Whisk continually, until the egg mixture is pale yellow, thick and creamy. This will take about 8-10 minutes. Do not give up! When the thermometer reaches between 145°F to 150°F remove the bowl from the simmering pot and set the bowl into the prepared ice-water bath. Continue to whisk the egg mixture until it has cooled completely. 

Stir the cooled coffee mixture into the egg mixture.

Remove the chilled bowl and the beaters from the freezer and add the cream and the remaining 1/4 cup sugar. Beat the mixture to the stiff-peak stage. Stir 1/3 of the whipped cream into the egg-coffee mixture, then using a spatula, fold the remaining whipped cream into the egg-coffee mixture. Be gentle so as to not deflate the whipped cream but continue to fold until there are no visible white streaks.

Remove the cups from the refrigerator and portion 1/2 cup the mixture into each of them filling to within 3/4-inch from the rim. Transfer the filled cups to the freezer and freeze for at least 6 hours. Overnight is best. 

To a pre-chilled small bowl, add the 1/2 cup of cream, the sour cream, vanilla and sugar. Whip the mixture to the soft-peak stage. Cover the dish and refrigerate until serving the dessert.

Remove the cups of Cappuccino Semifreddo from the freezer and spoon the frothy whipped cream on each dessert to the top of the cup. Smooth to a thick layer. Using the finest mesh sieve possible, sift a light dusting of espresso powder on each dessert. Enjoy!