Brew the espresso and let it cool, then mix in the Marsala wine or dark rum. In a bowl, whisk the egg yolks with the sugar until pale and thick. Fold in the mascarpone until smooth. In a separate bowl, whisk the egg whites until they form stiff peaks, then gently fold them into the mascarpone mixture. Quickly dip each ladyfinger into the coffee mixture (do not soak), and layer them in a dish. Spread half the mascarpone mixture over the ladyfingers. Repeat with another layer of dipped ladyfingers and the remaining mascarpone. Smooth the top, cover, and chill for at least 6 hours or overnight. Before serving, dust generously with cocoa powder.