Preheat the oven to 350 degrees F. Line 2 sheet pans with parchment paper.

In a medium bowl, stir together the flour, cocoa, baking soda and baking powder. Set aside.

In a large bowl, melt 10 tablespoons of the butter in the microwave. Cut the remaining 4 tablespoons butter in to 6-8 pieces and stir into the melted butter. Allow the butter to cool for 5-10 minutes (it should be about 90-95 degrees which is warm to the touch, not hot.)

Combine the melted butter, brown sugar, vanilla and salt in the bowl of an electric mixer. Mix for about 1 minute on medium speed or until smooth. Add the egg and egg yolk and mix for about 30 seconds or until smooth.

With mixer on low speed, add flour and mix just until combined and flour is incorporated. Add chocolate chips and mix just until incorporated.

Place demera (or turbinado) sugar in a shallow bowl.

Roll the dough into balls, about 2-3 tablespoons for each cookie. Roll the balls in the derma sugar and place on prepared baking sheets. Using the bottom of a glass, flatten the cookies slightly and sprinkle with a bit more demera sugar.

Bake the cookies, one sheet at a time, until they have puffed and have cracks running through the top, about 12-14 minutes. Be careful not to over bake the cookies or they will be dry. Transfer the cookies to a wire rack to cool completely.