1. Make the coffee syrup: mix hot coffee with the liqueur, pour into a large dish and set aside to cool.
2. Make the filling: place egg yolks and sugar in a large heatproof bowl and set over pot with simmering water (bain marie). Make sure the bottom of the bowl does not touch the water. start whisking constantly, until the sugar is dissolved, and the custard thickens. The temperate of egg yolk should reach 154-158ºF (68-70ºC). This step is optional (read notes). remove the bowl from heat and let cool.
3. Add the mascarpone, vanilla extract and whisk until smooth.
4. In a separate bowl whip cold heavy cream to stiff peaks. Fold 1/3 of the whipped cream into the mascarpone mixture. Then the remaining whipped cream. Set aside.
5. Assemble: dip each ladyfinger into the coffee mixture for 1-2 seconds. Place in the bottom of a 9x13 inch (22X33cm) dish. If needed, break a few ladyfingers to fit them in the dish. Spread half of the cream over the soaked ladyfingers. Repeat with another layer of ladyfingers and spread the remaining cream on top. Cover and refrigerate the tiramisu for at least 6 hours.
6. Just before serving, dust with cocoa powder.
• Whisking the egg yolks with the sugar over the bain marie is optional. Traditionally, whisking the raw eggs yolks with sugar its totally fine. If you use fresh eggs, there is no danger. But, many people intimidate eating raw eggs so it’s up to you.
• Instead of heavy cream you can use 4 egg whites. Beat to stiff peaks, then fold to the mascarpone mixture. This is the Italian traditional way. But, I find that the version with the heavy cream richer and much better. But, again, it’s up to you.