1 1/4 cups all-purpose flour
1/3 cup unsweetened cocoa powder
1/2 teaspoon baking soda
1 stick plus 3 tablespoons (11 tablespoons) unsalted butter, at room temperature
2/3 cup packed light brown sugar
1/4 cup sugar
1/2 teaspoon fleur de sel or 1/4 teaspoon fine sea salt
1 teaspoon vanilla extract
5 ounces bittersweet chocolate, chopped into chips, or a generous 3/4 cup store-bought mini chocolate chips