Place the chopped chocolate in a large bowl. In a saucepan, bring the cream to a simmer over medium-high heat. Quickly pour the hot cream over the chocolate and let sit for 1 minute; then whisk together until the chocolate is melted. Whisk in the mascarpone, then strain into a bowl big enough to whip the mixture in the next day. Cover and refrigerate at least 6 hours or overnight.
Remove the chocolate mixture from the refrigerator and whip until fluffy and slightly stiffened, being careful not to overwhip (like heavy cream, the mixture can turn to butter if whipped too long). Refrigerate.
Combine the espresso and coffee liqueur in a shallow dish. (I wear rubber gloves for the next step to keep my fingers from getting stained). Pick up 1 ladyfinger, then place it in the espresso for just as long as it takes you to pick up the next 1 and place it in the espresso (about 10 seconds). Fish the first 1 out and place it in the bottom of a 9 by 13-inch baking dish. Repeat with the remaining ladyfingers, arranging them in rows in the bottom of the dish and continuously adding and removing the ladyfingers from the espresso mixture. (This will allow them to soak for the perfect amount of time without getting soggy--they should be wet on the outside but still have an unsoaked core at the center.)
When you have made a complete layer of ladyfingers, spread half of the chocolate mixture over the ladyfingers and cover lightly with some of the chocolate shavings. Repeat, making 1 more complete layer of ladyfingers, chocolate, and shavings. Cover and refrigerate until ready to serve, at least 2 hours.
Serve cold, dishing out spoonfuls with a large serving spoon. Sprinkle with powdered sugar, if desired.