Tiramisu

Method

1. In a heatproof bowl set over a pot of gently simmering water (not touching the water), whisk the egg yolks and sugar together until pale.
2. Gradually whisk in the milk and continue whisking constantly over the simmering water for 8 to 10 minutes, until the mixture thickens enough to coat the back of a spoon and reaches 160 F.
3. Remove from heat and let cool to room temperature, whisking occasionally to prevent a skin from forming.
4. Whisk the mascarpone into the cooled custard until smooth and no lumps remain.
5. In a separate bowl, whip the heavy cream to stiff peaks, then gently fold it into the mascarpone mixture in two additions until fully combined and airy.
6. Combine the cooled espresso and coffee liqueur, if using, in a shallow dish.
7. Quickly dip each ladyfinger into the espresso mixture for about 1 second per side -- do not soak, or they will turn mushy -- and arrange in a single layer in a 9x13-inch dish.
8. Spread half of the mascarpone cream evenly over the ladyfingers.
9. Repeat with a second layer of dipped ladyfingers and top with the remaining mascarpone cream, smoothing the top.
10. Cover and refrigerate for at least 4 hours, preferably overnight, to let the layers set and the flavors meld.
11. Just before serving, dust generously with cocoa powder through a fine sieve.