For the frosting, whisk 1 to 1 1/2 tablespoons of the remaining espresso extract into the remaining mascarpone filling. Taste the frosting as you go to decide how much extract you want to add. If the frosting looks as if it might be a little too soft to spread over the cake, press a piece of plastic wrap against its surface and refrigerate it for 15 minutes or so. Refrigerate the cake too.
With a long metal icing spatula, smooth the frosting around the sides of the cake and over the top. If you want to decorate the cake with chocolate-covered espresso beans, press them into the filling, making concentric circles of beans or just putting some beans in the center of the cake.
Refrigerate the cake for at least 3 hours (or for up to 1 day) before serving – the elements need time to meld.
Just before serving, dust the top of the cake with cocoa.
(Though the cake recipe looks exhaustive it turned out to be quite simple when I actually made it)
Check out the roundup for more scrumptious versions of this cake at A sweet Punch