Whisk mascarpone cheese, sugar, and amaretto liqueur together in a bowl until smooth.
Beat cream in a glass or metal bowl until soft peaks form. Lift your beater or whisk straight up: whipped cream should form soft mounds rather than a sharp peak. Fold whipped cream into mascarpone mixture. Pour espresso into a separate bowl.
Dip 12 ladyfingers into espresso; arrange dipped ladyfingers in an 8-inch square baking pan. Spread ½ mascarpone mixture over ladyfingers; grate 1 chocolate square over mascarpone layer. Dip remaining 12 ladyfingers into espresso; arrange dipped ladyfingers on top. Spread remaining ½ mascarpone mixture over ladyfingers; grate remaining 1 chocolate square over mascarpone layer. Refrigerate tiramisu until set, at least 2 hours.
