Combine the espresso and syrup. Brush the sponge sheets generously with this syrup, using it all.
Place one sponge sheet on a tray. Spread half the filling evenly over the sponge.
Top with the second layer of sponge, followed by the remaining filling. Smooth the top. Chill.
Dust the top with cocoa powder.
Cut 6 × 4 into 24 portions.
Note: This recipe is easily cut in half. Start with a half-size sponge sheet and use half the filling and coffee syrup. Alternatively, use ready-prepared ladyfinger cookies in place of the sponge sheet.