Instructions

• Preheat the oven to 350 degrees Fahrenheit and line 2 baking sheets with parchment paper.
• Make the streusel: in a small bowl whisk together 6 tablespoons all-purpose flour, 2 tablespoons granulated sugar, 2 tablespoons packed brown sugar, ½ teaspoon ground cinnamon, and ⅛ teaspoon salt.
• Add 3 tablespoons cold unsalted butter to the flour mixture and cut it in with a pastry cutter, fork, or clean hands until the mixture forms coarse crumbs with no large pieces of butter. Cover and refrigerate the streusel until the cookie dough is ready to be topped.
• Make the cookie dough: in a large bowl, beat ½ cup room-temperature unsalted butter, ½ cup packed brown sugar, and ⅓ cup granulated sugar on medium-high speed with a hand mixer or stand mixer fitted with the paddle attachment for 3–4 minutes, until light and fluffy.
• Add 1 large room-temperature egg and ½ teaspoon vanilla extract to the butter mixture and mix until combined, scraping down the sides and bottom of the bowl as needed.
• In a medium bowl sift or whisk together 2 cups all-purpose flour, 2 tablespoons cornstarch, 1 teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon ground cinnamon, and ½ teaspoon salt.
• Add the dry ingredients to the butter mixture and mix until just combined. The dough will be fairly dry and crumbly.
• Use a medium cookie scoop (about 2½ tablespoons) to portion the dough, pressing the dough into the scoop to compact it if needed. Place the scoops on the prepared baking sheets about 2 inches apart.
• Use the back of the cookie scoop (or your thumb) to gently press an indent into the center of each cookie dough mound.
• Remove the chilled streusel from the refrigerator and fill each cookie indent with a generous amount of streusel, pressing lightly so it adheres.
• Bake the cookies for 11–13 minutes, until the edges are set. (The cookies will not brown much, so do not wait for browning.)
• Let the cookies cool on the baking sheet for 2–3 minutes, then transfer them to a cooling rack to cool completely.
• When the cookies are completely cool, make the glaze: whisk together ¾ cup powdered sugar, 2 tablespoons milk, and ¼ teaspoon vanilla extract (optional) until smooth. If the glaze is too thick, add a little more milk at a time; if it is too thin, add a little more powdered sugar at a time until you reach the desired consistency.
• Drizzle the glaze over the cooled cookies before serving.