Line a loaf pan with plastic wrap, leaving at least 3 inches overhang.
To prepare the ice cream, in a medium saucepan, combine milk, heavy cream, 1/4 cup sugar and salt. Bring mixture to simmer, stir until sugar is dissolved. Remove from heat and set aside.
Whisk egg yolks and remaining sugar in a medium bowl until pale, about 2 minutes. Gradually whisk in half of the warm cream mixture, mix until blended. Stir yolk mixture into the remaining cream mixture. Cook over medium heat, stirring constantly, until thick enough to coat a wooden spoon, about 2 to 3 minutes.
Add Mascarpone cheese and stir until completely melted and mixture is smooth.
Strain custard into another medium bowl. Let cool over a bowl of ice water, or chill in the refrigerator, stirring occasionally.
Process the mixture in an ice cream maker according to manufacturer’s instructions.
To assemble, dip ladyfingers, one at a time, into the espresso and arrange in a single layer on the bottom of the prepare loaf pan. Spread 1/3 of the ice cream over the ladyfingers. Dust 1/3 of the cocoa powder on top. Then another layer of ladyfingers, mascarpone filling, cocoa powder, ladyfngers and mascarpone filling.
Place the pan in freezer to firm up, at least 30 minutes.
To serve, lift cake from pan using plastic wrap overhang. Place cake upside down on a serving plate. Remove plastic wrap. Dust top of cake with cocoa powder. Slice and serve.