Stir the espresso with Marsala or rum if using. Let it cool.

In a heatproof bowl over barely simmering water, whisk yolks, sugar, and a pinch of salt for 6 to 8 minutes until thick and pale.

Remove from heat and cool for 5 minutes before adding mascarpone.

Whisk the mascarpone into the yolk mixture until smooth and silky.

Fold the whipped cream into the mascarpone mixture in two additions until fluffy and uniform.

Dip ladyfingers into the espresso for about 1 second per side and line a 9x13 dish with a snug layer.

Spread half the cream on top and repeat with another layer of dipped ladyfingers and the remaining cream.

Cover and refrigerate for at least 6 hours, preferably overnight.

Just before serving, dust generously with cocoa powder.

Slice and serve cold.