Preheat the oven to 160 ° C. Line a 24cm springform pan with baking paper.
1 Whisk the yolks and ½ cup caster sugar for 5 minutes with an electric mixer on a high speed until it is a pale yellow. 2 Reduce the mixer speed and add the olive oil in a thin stream. Continue whisking until all the oil is added. 3 Add the whole wheat flour, baking powder and hot chocolate and mix well. Finally, add the water to the batter and mix well. 4 Whisk the egg whites in a separate bowl until soft peak stage. Add the 50 g caster sugar a little at a time, beating until the egg whites are shiny and smooth. Fold the beaten egg whites gently into the cake mixture. 5 Pour the mixture into the prepared tin and bake for ± 1 hour. Let the cake cool and dust with dry hot chocolate powder.