Combine mascarpone cheese, sugar, and amaretto liqueur in a bowl and whisk until velvety smooth.
Whip cream in a glass or metal bowl until soft peaks form. Test by lifting the beater or whisk straight up: whipped cream should form soft mounds instead of sharp peaks. Gently fold whipped cream into mascarpone mixture.
Start by pouring espresso into a bowl. Dip ladyfingers into the espresso and place 12 dipped ladyfingers in an 8-inch square pan. Spread half of the mascarpone mixture over the ladyfingers. Grate one chocolate square over the mascarpone layer. Repeat with another layer using the remaining dipped ladyfingers, mascarpone mixture, and chocolate. Refrigerate the tiramisu until set, for at least 2 hours.