½ pound (2 sticks) unsalted. butter, melted and still warm. ¾ cup packed light brown sugar. ½ cup granulated sugar. 2 tablespoons nonfat milk powder. 1 large egg. 1¾ cups all-purpose flour. 1¼ teaspoons kosher salt. 2 teaspoons vanilla extract. ½ teaspoon baking powder. ¼ teaspoon baking soda. 1 (12-ounce) bag semisweet chocolate chips.