In a large mixing bowl, combine the mascarpone cheese, heavy cream, granulated sugar, vanilla extract, and a pinch of salt. Using an electric mixer, beat on medium speed until the mixture is smooth and 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 baking dish, arrange a layer of soaked ladyfingers at the bottom. Spread half of the mascarpone mixture over the ladyfingers, smoothing it out evenly.

Repeat the process with another layer of soaked ladyfingers followed by the remaining 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 using.