1tspflaked saltsuch as Fleur de Sel, Maldon's etc.
Preheat oven to 350F (not fan-assisted), with rack in centre of oven.
In a medium bowl, whisk together the all purpose flour, cocoa, baking powder, baking soda and salt
In a large bowl with an electric mixer or with a stand mixer fitted with the paddle attachment, cream together the butter, brown and white sugar at medium-high speed until light and fluffy, about 2-3 minutes. Scrape down the bowl once or twice. Add the egg and vanilla and mix in. Add the flour mixture and mix until incorporated. Stir in the chopped chocolate.
Using a cookie scoop or a tablespoon measuring spoon, scoop out balls of dough and plate 2" apart on a parchment lined baking sheet. Top with a sprinkling of flaked salt.
Bake for 10-12 minutes, being sure not to over-bake. Cookies may look soft in the centre still, but that is fine. They will set further as they cool. Remove from oven and let cool on the baking sheet for about 5 minutes, then transfer to a cooling rack to cool completely.
Store in an airtight container once cooled. Will keep well for about a week or freeze for longer storage. *You can also freeze the unbaked dough. Portion into dough balls and then bake from frozen, topping with salt before baking and allowing an extra minute or two of baking time.
Be sure to read the Ingredient Notes and Baker's Tips above the Recipe Card for more tips on making this recipe.