Preheat the oven to 175°C (350 degrees F) and line a baking sheet with parchment paper.
Cream the butter and both sugars with an electric mixer for 3 minutes on medium-high speed.
Add the egg and vanilla extract. Mix for 1 minute.
Add in the flour, bicarbonate soda and salt, mix on low speed for a few seconds until just combined.
Fold in 50 grams of both chocolates, leaving some to top the cookies.
Use an ice cream scoop to scoop the cookie dough on the prepared sheet or shape it into balls by hand.
Bake for 9 minutes, take them out of the oven, place the remaning chocolate on top of the cookies and return to the oven for additional minute or two. Cookies should just slightly start to brown at the edges. They will maybe look not done yet but do not over-bake them!
Take out of the oven and leave to cool completely.