Method
Prepare Coffee

Combine coffee, vanilla extract and a tablespoon of sugar in a wide, small bowl. Allow to cool.

Prepare Filling

Beat egg yolks, and 3 tablespoons of sugar in a bowl set over a saucepan of barely simmering water until tripled in volume, 5 to 8 minutes.

Use a whisk or, to make things easier, a handheld electric mixer at medium speed. (Do not stop beating until removed from the heat).
Remove bowl from heat then beat in mascarpone cheese until just combined.  Set aside.

Whip cream in a bowl until it holds stiff peaks. Once the yolk and mascarpone mixture has cooled a little, gently fold in the whipped cream, half at a time.

Assemble Tiramisu

Dip half of the ladyfingers very quickly into the coffee, and line the bottom of a 9-inch square dish.
Spoon half of the mascarpone filling over the lady fingers and spread into an even layer. Sprinkle the cocoa powder over filling.

Dip the remaining ladyfingers very quickly into the coffee and arrange a second layer.
Spoon remaining mascarpone mixture over ladyfingers. Sprinkle more cocoa on top.  You can repeat the above steps if you want to include more layers.

Cover with cling film. leaving space at the top and refrigerate.  6 hours is recommended but I tried 4 and the consistency of cream and sponge was just right.

When ready to serve, dust with extra cocoa powder. Leave out at room temperature about 20 minutes before serving. (Tiramisu can be chilled up to 2 days, but no longer or else the ladyfingers will break down too much).