Mix the egg yolk, half of the sugar and the liquid glucose. As the mixture thickens, add a little gradually add the water until it is a soft and firm structure (duration: about 15 minutes).
mix the flour, the roasted and ground hazelnuts, the cocoa and the vanilla by hand. Sieve out the hard pieces and add to the egg yolk mixture using a spatula.
Beat the egg white and add the rest of the sugar when the egg whites start to set. mix the egg yolk and white carefully using a spatula.
Divide over baking trays of 60 x 40 cm and bake in a convection oven at 180 °C for 15 minutes with open key.