Start by breaking your chocolate bar in smalls pieces, do not mix them and use a different plate for each chocolate
Take a bowl, add the sugar and the soft butter and mix it with clean hands. You will then add the egg to obtain a nice mixture.
In the same bowl add the flour + the baking powder, mix to obtain a beautiful dough.
Take your dough, put it on the scale and divide it in two different doughs.
In one bowl, mix the dough with the dark chocolate and the cocoa powder. In another mix the other half of the dough with white chocolate.
Preheat your oven up to 180°C (350°F), and prepare your baking sheet. You will now take a small ball from each dough and combine it together to form your bi-choco cookie! (aprox 80g a cookie or even less) When everything is ready, put it in the oven for 10-12 min your white part doesn’t need to be too gold.