Split cakes into two. Spread a thin layer of buttercream on the cake board.
Place the first layer of sponge on a 8 inch thin cake board, flat size down. Brush the cake with coffee syrup using a pastry brush (repeat this process with remaining layers of cake).
Place one layer of cake, flat side down on top and plop a big dollop of mascarpone cream in the middle. Spread the mascarpone cream carefully. Once it is nice and flat, stack the second cake, flat side down and spread another generous amount of mascarpone cream then repeat with the third cake. Then place final cake, flat side down.
Spread a thin layer of coffee frosting on the sides and then top of cake. It helps to use a turntable when frosting a cake. Hold a scraper flat against the side of the cake and then turn the turntable and scraper to make a nice, smooth coat of buttercream. Smooth the top of cake with scraper, drawing the peaks off the top edges of cake into the centre.
Chill crumb coated cake in fridge for 30 minutes until buttercream is nice and firm.
Once cake is chilled, cover evenly with buttercream using an off set spatula and then use a scraper to smooth the edges. Pipe decorative borders if desired. Dust the top of the cake with cocoa powder.