Ingredients:
6 large egg yolks
1 cup sugar
6 tbsp dark rum optional
1 1/2 cups mascarpone cheese, cold
1 cup heavy whipping cream, cold
1 cup boiling water
1 tbsp instant espresso powder
1 package ladyfingers
Cocoa powder for dusting the top

Method:

• Whip together egg yolks and 3/4 cup sugar until very pale yellow and about tripled in volume. Transfer mixture to a large bowl, wiping out the medium bowl used to whip the yolks and set aside.
• Gradually whisk in 4 tbsp of the rum and continue whisking rapidly over the double boiler for about 10 minutes. Keep aside to cool down to room temperature. This is your zabaglione.
• With a hand mixer or in the bowl of a stand mixer with a whisk attachment, beat the mascarpone on medium speed for 15 to 30 seconds, until it smooths out and softens. Be careful not to over-beat or else the mascarpone will separate and become grainy.
• Gradually add the cream in a thin, slow stream until it’s all incorporated. This should take 1 to 2 minutes. Continue beating with the mixer on medium-high speed for another 30 to 60 seconds, until the mixture holds firm, not-quite-stiff peaks.
• Now fold 1/3 of the whipped cream into the zabaglione to lighten it, then fold in the remaining whipped cream.
• Assemble the tiramisu: Combine espresso with hot water and quickly dip each ladyfinger into the espresso mixture and place them rounded side up at the bottom of a greased baking dish. Arrange the dunked ladyfingers in rows on the bottom of the baking dish. Spread half the mascarpone mixture onto the ladyfingers in one even layer. Repeat dunking and arranging a second layer, and spread the remaining mascarpone over top. Dust top layer with remaining tablespoon of cocoa powder. Cover the tiramisu and refrigerate for at least 8 hours or up to 24 hours to give the tiramisu time to firm up and for the ladyfingers to soften. Re-add cocoa powder dusting on top while serving again if needed.

Tip: You can substitute the egg yolk & sugar by using 1/2 cup of custard powder instead.