Preheat the oven to 200°C/400F. Grease and line a 23x30cm rectangular tin. Beat the eggs with the confectioner’s sugar until they become glossy and smooth. Melt the butter and add it to the eggs, along with the flour and baking powder. Mix well. Divide the mix into two parts. Pour the first into the tray and put in the oven. As soon as it starts to become golden, remove it from the oven and carefully roll it up, using a clean kitchen cloth to help. Unroll the cake and leave to rest. Take the second half of the mix, add the cocoa, and pour into clean tray. Bake as for the first. When ready, remove from the oven and leave to cool for 5 minutes. Position the cocoa cake on top of the first and spread the surface evenly with Nocciolata. Roll both cakes together in upon themselves. The heat of the second cake will help the layers to adhere. Dust with cocoa and wrap with plastic wrap to keep secure while the cake cools. When cold, slice into rounds of about 1cm. Take each slice and dip in melted chocolate and leave to cool on a wire rack.