Place the eggs and water in a mixer with whisk, add the Pan di Spagna 50 sponge mix, flour, sugar and cocoa and mix at a low speed to form an even dough. Whisk at high speed for around 10 minutes. Pour the mix into a pre-greased mould until three-quarters full. Bake in a fan-assisted oven at 160°C or in a static oven at 180°C for 23-25 minutes.