2 1/4 cups (280 g) all-purpose flour
3/4 teaspoon baking soda
3/4 teaspoon salt
1 cup (2 sticks) unsalted butter, at room temperature
3/4 cup (150 g) packed dark brown sugar
3/4 cup (150 g) granulated sugar
4 large egg yolks, at room temperature
1 teaspoon vanilla extract
6 oz semisweet or bittersweet chocolate, chopped into shards
1 large egg, lightly beaten (for egg wash)
1/4 teaspoon fleur de sel (optional)