How to Make It
In a small saucepan, combine 1 cup of the sugar with 3/4 cup of water and 1/4cup of the espresso. Bring to a simmer over moderate heat and stir to dissolve the sugar. Let the espresso syrup cool.
In a small saucepan, boil the remaining 1 cup of espresso over high heat until reduced to 1/4 cup, about 8 minutes. Pour into a medium heatproof bowl. Rinse and dry the saucepan.
In the same saucepan, warm the milk with the vanilla bean and seeds over moderate heat until bubbles form around the edge, about 2 minutes. Remove from the heat and stir in the gelatin mixture until melted. Discard the vanilla bean. Add the hot milk to the reduced espresso and whisk in the chocolate until melted.
In the bowl of a standing mixer, beat the eggs at high speed until light yellow and foamy. In the small saucepan, bring the corn syrup, the remaining 1/2 cup of sugar and 2 tablespoons of water to a simmer. Cook over moderately high heat until the syrup registers to 235° on a candy thermometer, about 5 minutes. With the mixer at medium high speed, gradually beat the hot syrup into the eggs. Continue beating until the mixture is very pale and has tripled in volume, about 4 minutes. Fold in the espresso mixture.
In a bowl, whip the heavy cream until stiff peaks form. Fold into the mousse mixture until no streaks remain.
Spoon about one-fourth of the espresso mousse into a 9-inch springform pan. Dip 6 lady fingers into the espresso syrup until just soaked through. Arrange the lady fingers over the mousse in rows. Repeat the process two more times with the mousse and the remaining lady fingers, then top with the remaining mousse. Cover with plastic wrap and freeze for at least 6 hours.
Before serving, warm a thin sharp knife under hot water. Run the knife around the edge of the semifreddo and remove the ring. Sift the cocoa over the top of the semifreddo. Cut the semifreddo into wedges and serve, garnished with raspberries.
A dollop of unsweetened whipped cream.