It is best to start by making the cookie dough first. To do so, cream the egg, yolk, white sugar, and brown sugar together before slowly adding the oil while continuing to stir. Mix together the flour and baking powder before combining with the egg mixture. Finally, add the chocolate drops and chill the dough.
For the brownie batter, melt the dark chocolate in a pan, add the oil and stir. Allow the mixture to cool. Beat the egg and sugar until frothy, then stir in the flour gradually. Add to the chocolate mixture and the ground hazelnuts before combining everything well.
Grease a rectangular tin with Byodo Baking Spray Oil. Pour in the brownie batter and smooth out. Take the cookie dough out of the fridge and roll out to form a rectangle the size of the tin. Position the dough on top of the batter.
Bake the brownie batter in a preheated oven for 30-35 minutes at 175 °C.