Chop the chocolate into rough pieces. I broke the feves into halves and thirds by hand. Set aside.
In a medium bowl, sift together the flour, cocoa and baking soda.
Place the butter in a bowl and use a spatula to soften. Add the chocolate, sugars, fleur de sel and vanilla and mix well.
Add the flour mixture to the butter mixture until combined, without overworking.
Divide the dough into two equal parts and roll each piece into a log shape.
Wrap each piece in plastic wrap and refrigerate for at least two hours.
Preheat the oven to 335ºF and prepare two large baking sheets with silicone mats, or parchment.
Remove the dough from the fridge and peel off the plastic film.
Slice the logs into 1cm-thick discs. Place the discs on the silicone-lined baking sheets and bake for 11-12 minutes. Remember: it’s important that you don’t overcook them.
Remove from the oven and sprinkle with with a little fleur de sel.
Notes
DO NOT OVERBAKE! The original recipe yields 40-60 cookies, I made my logs a little bigger (two, instead of three) for larger cookies.The original recipe calls for brown sugar which I used for one batch, and experimented with date and pepper red sugar for another batch. They both turned out great, but I rather liked the latter.