Brew the coffee or espresso and let it cool to room temperature. Stir in 1 tablespoon of cocoa powder and sugar if using.
In a large bowl, whip the heavy cream until it starts to hold soft peaks.
In another bowl, mix mascarpone, powdered sugar, and vanilla until smooth. Gently fold in the whipped cream.
Dip each ladyfinger into the coffee briefly—just enough to soak but not fall apart.
Layer half the soaked ladyfingers in an 8x8-inch dish.
Spread half the mascarpone mixture over the top. Dust with a bit of cocoa powder.
Repeat with another layer of dipped ladyfingers and the remaining mascarpone.
Chill for at least 4 hours or overnight. Dust with remaining cocoa and sprinkle shaved chocolate on top before serving.