8 oz. semisweet chocolate, coarsely chopped
4 tbsp. unsalted butter
2/3 cup all-purpose flour
½ tsp. baking powder
¾ tsp. fleur de sel (sea salt), plus more for sprinkling
2 large eggs, at room temperature
¾ cup packed light brown sugar
1 tsp. vanilla extract
12 oz. semisweet chocolate, coarsely chopped
Preheat the oven to 350˚ F. Line two baking sheets with parchment paper or silicone baking mats.
Combine the 8 ounces chopped chocolate and butter in a heatproof bowl set over a pan of simmering water, and heat until the chocolate and butter are melted and smooth, stirring occasionally. (Alternatively, heat in the microwave in 25-second intervals, stirring in between.) In another mixing bowl, stir together the flour, baking powder and salt.
In the bowl of an electric mixer, combine the eggs, brown sugar and vanilla. Beat on medium-high speed until the sugar has completely dissolved, about 4-5 minutes. Reduce the speed to low and add the melted chocolate mixture, blending until incorporated. Add in the dry ingredients and mix just until combined. Fold in the remaining chopped chocolate with a spatula. Drop heaping tablespoons of dough onto the prepared baking sheets, about 2-3 inches apart (I used my medium-sized dough scoop).
Bake, rotating the baking sheets halfway through, until the cookies are just slightly soft in the center and crackly on top, about 10-12 minutes. Sprinkle lightly with additional salt and let cool on the baking sheets 10 minutes. Transfer to a wire rack to cool completely. Store in an airtight container.