In a large bowl, using an electric mixer with whisk attachment, beat egg yolks and sugar until thick and pale, about 5 minutes. Add mascarpone cheese and beat until smooth. Add 1 tablespoon of espresso and mix until thoroughly combined.
In a small shallow dish, add remaining espresso and rum. Dip each ladyfinger into espresso for only 5 seconds. Letting the ladyfingers soak too long will cause them to fall apart. Place the soaked ladyfinger on the bottom of a 13 by 9 inch baking dish, breaking them in half if necessary in order to fit the bottom.
Spread evenly 1/2 of the mascarpone mixture over the ladyfingers. Arrange another layer of soaked ladyfingers and top with remaining mascarpone mixture.
Cover tiramisu with plastic wrap and refrigerate for at least 2 hours, up to 8 hours.
Before serving, sprinkle with chocolate shavings.
Contains Raw Eggs: The Food Network Kitchen suggest caution in consuming raw and lightly cooked eggs due to the slight risk of salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly refrigerated, clean grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell. For recipes that call for eggs that are raw or undercooked when the dish is served, use shell eggs that have been treated to destroy salmonella, by pasteurization or another approved method.