Combine the espresso powder and boiling water, stir until incorporated. Set aside to cool completely or pop it in the refrigerator.
Using an electric mixer, beat together the mascarpone cheese and powdered sugar on medium speed until smooth. Set aside.
Whisk together the heavy cream, and rum liqueur on high speed until stiff peaks form. Gently fold in the mascarpone mixture
Lightly dip, instead of soaking the ladyfingers in the espresso one at a time. Line the bottom of a 6×8 pan. Using a spatula, spread half of the cream mixture over the biscuit. Sprinkle shaved chocolates on top. Layer the remaining biscuit and spread the other half of the cream mixture on top.
Smooth the top using a spatula. Sift the cocoa over the top and sprinkle more chocolates. Cover the pan with a cling wrap and refrigerate for 3 to 4 hours or until set.
*It tastes even better when left overnight in the refrigerator.