Grease and line with baking paper two large trays.
Preheat the oven to 180 º C.
In the microwave or over a water bath melt the chocolate with the butter. Set aside.
In a separate bowl, mix the flour, cocoa powder, and salt.
With a mixer, beat the egg and sugars for about 5 minutes. The mixture should be about double in volume.
Slowly pour in the melted chocolate until it is fully incorporated.
Then lower the speed of the mixer to the lowest setting and add the dry ingredients.
Lastly, fold in the chocolate drops and chopped walnuts.
With an ice cream scoop, remove portions of the dough. Make about 18 to 20 cookies of the same size, split between the 2 trays. Slightly flatten the top of each cookie.
Bake for about 8 to 12 minutes. The cookies are ready when they have cracked top, similar to a brownie.
Before serving, sprinkle a dash of fleur de sel on each cookie. They are even better served warm with a side of ice cream!