In a large mixing bowl, combine the mascarpone cheese, heavy cream, powdered sugar, and vanilla extract. Use an electric mixer to whip the mixture until it forms soft peaks, about 3-5 minutes.

In a shallow dish, pour the cold brew coffee. Quickly dip each ladyfinger into the coffee, ensuring they are soaked but not soggy.

In a 9x9-inch dish, layer half of the soaked ladyfingers at the bottom. Spread half of the mascarpone mixture over the ladyfingers.

Repeat with the remaining ladyfingers and mascarpone mixture.

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.

Before serving, dust the top with cocoa powder and sprinkle with grated dark chocolate if desired. Serve chilled.