Brew the espresso and let it cool to room temperature. Stir in the marsala or rum, if using, and pour into a shallow dish.

Whisk the egg yolks with half the sugar (50 g) in a heatproof bowl until pale.

Set the bowl over a pan of gently simmering water, not touching it. Whisk constantly for 3 to 4 minutes until thick and the mixture reaches 160 F / 71 C.

Remove from the heat and keep whisking off the heat for about 2 minutes until cooled slightly.

Beat the mascarpone into the cooled yolk mixture until smooth with no lumps.

In a clean, dry bowl, whisk the egg whites with a pinch of salt to soft peaks. Add the remaining sugar (50 g) and whip to stiff, glossy peaks.

Fold the egg whites into the mascarpone mixture in three additions, working gently until no white streaks remain.

Dip each ladyfinger in the cooled coffee for 1 second per side, don't soak, and arrange in a single layer in a 9x13 inch dish.

Spread half the mascarpone cream evenly over the ladyfingers.

Repeat with a second layer of dipped ladyfingers, then top with the remaining cream and smooth the surface.

Cover and chill for at least 6 hours, ideally 12 to 24 hours, until fully set and sliceable.

Dust generously with cocoa powder through a fine-mesh sieve just before serving.