To assemble the cake:
Place one of the chocolate cakes onto your serving platter of cake stand, top it with half of the mascarpone filling and use a palette knife to spread it out evenly over the surface of the cake. Place the 2nd cake on top and cover with the remaining mascarpone filling mixture before topping it with the final chocolate cake.
Using a clean palette knife, spread some of the ganache frosting over the sides of the cake, then spread the remainder over the top ensuring that it, and the sides, are evenly covered – warming your knife slightly beforehand can make this job easier.
Sprinkle the top with the candied pecans (or white chocolate shavings) and serve!