Make the Dough: Adjust oven rack to middle position and preheat to 350°F (180°C). Set aside a handful of chopped chocolate (about 2 ounces; 55g) and place the remainder in a medium bowl. Sift flour on top and toss together. Combine butter, white sugar, brown sugar, vanilla, salt, baking soda, baking powder, and nutmeg in the bowl of a stand mixer fitted with a paddle attachment. Mix on low to moisten, then increase to medium and beat until light and fluffy, about 5 minutes. With mixer running, add egg and continue beating only until smooth. Reduce speed to low, add flour/chocolate all at once, and mix to form a stiff dough.

Portion the Dough: Divide in 2-tablespoon portions (about 1 1/2 ounces or 40g each) and round each one into a smooth ball. (If you like, portioned dough can be refrigerated in a heavy-duty zipper-lock bag up to 1 week, or frozen 6 months. Stand at room temperature until quite soft, about 70°F or 21°C, and proceed as directed.)

To Bake: Arrange portions on a parchment-lined half sheet pan, leaving 2 inches between cookies to account for spread. Garnish each with reserved chocolate and a pinch of kosher salt. Bake until puffed and pale gold around the edges but steamy in the middle, about 15 minutes. For crunchy cookies, continue baking until golden, 3 to 5 minutes more. Cool directly on baking sheet until crumb is set, about 5 minutes. Enjoy warm or store in an airtight container up to 2 days at room temperature.