In a large bowl using an electric mixer with a whisk attachment beat egg yolks and sugar until thick, 5 minutes; add mascarpone cheese; beat until smooth; add 1 tablespoon of espresso; mix until thoroughly combined
In a shallow dish, add remaining espresso and rum; dip each ladyfinger into espresso for 5 seconds; place the soaked ladyfinger on the bottom of a 13×9 inch baking dish
Spread evenly 1/2 of the mascarpone mixture over the ladyfingers; arrange another layer of soaked ladyfingers; top with remaining mascarpone mixture
Cover tiramisu with plastic wrap; refrigerate for 2 hours; before serving dust with cocoa and sprinkle with chocolate shavings