Melt 8 oz chopped chocolate with 4 tbsp butter in a double boiler until smooth and melted. Add flour, fleur de sel, and baking powder and mix until incorporated. In a mixer with the paddle attachment, beat eggs with the sugar and vanilla until the sugar is incorporated (about 2-3 minutes). Add in the flour and chocolate mixture. Fold in the remaining 12 oz of chocolate chips. Spoon out heaping tablespoons of the cookie dough on a lined cookie sheet.Sprinkle with fleur de sel and bake for about 10-12 minutes, rotating halfway through. Remove when the cookies have baked out and cracked a little. Let sit for a minute or two then remove and let cool on a wire rack. Nom with a glass of cold milk. OMNOMNOM. So good.