Line a cookie sheet with parchment paper and set aside.
In a medium bowl, stir together the flour, baking powder, baking soda, cinnamon, salt, and nutmeg until combined; set aside.
2 ¼ cups all-purpose flour, 1 ½ teaspoons baking powder, ½ teaspoon baking soda, ½ teaspoon ground cinnamon, ½ teaspoon fine sea salt, ¼ teaspoon ground nutmeg
In the large bowl of your stand mixer with the paddle attachment, cream the butter with the brown sugar until smooth.
¾ cup unsalted butter, ¾ cups light brown sugar
Add the egg, egg yolk, and vanilla and mix until combined.
1 large egg, 1 large egg yolk, 2 teaspoons vanilla extract
Add the flour mixture a little at a time until fully mixed in; scrape down the sides as needed.
Take two tablespoons of the dough and roll it into a ball, placing it on the prepared sheet tray. Repeat with the remaining dough.
Cover the tray with plastic wrap and place it in the fridge to chill for 2 hours.
Preheat the oven to 350°F. Line sheet trays with parchment paper and set aside.
To make the crumble, combine the brown sugar, flour, cinnamon, salt, and nutmeg in a small bowl and stir to combine.
3 tablespoons light brown sugar, ½ cup all-purpose flour, ¼ teaspoon ground cinnamon, Pinch of fine sea salt, pinch of ground nutmeg
Add the melted butter, and using a fork, stir it around until crumbles form.
4 tablespoons unsalted butter
Place the cookie dough balls onto the prepared sheet trays about 3 inches apart.
Gently press down the tops with the palm of your hand.
Using your fingers, make a small indention in the middle of the cookies to form a little pocket for the crumble.
Add the crumble to the center of the cookies, gently pressing it in to stick.
Bake for 10-12 minutes until the cookies appear dry on the tops and are lightly golden brown along the edges. Keep the cookies that are not baking in the fridge while you bake the others.
Cool on the tray for 10 minutes before transferring to a wire rack to cool completely.
Once cool, make the glaze by whisking the powdered sugar, milk, and vanilla until smooth. Start with 1 tablespoon of milk and add up to 1 more tablespoon if needed. The glaze should be thick yet pourable.
1 cup powdered sugar, 1-2 tablespoons milk, ½ teaspoon vanilla extract
Drizzle the glaze on the cooled cookies and let it set for at least 30 minutes to harden.
Notes
Chill the Dough: Don’t skip the chilling step. It helps the cookies keep their shape and develop the perfect texture.
Don’t Overbake: Keep an eye on the cookies and take them out when they’re just golden brown. Overbaking can make them too hard.
Use Fresh Spices: Fresh cinnamon and nutmeg will give your cookies the best flavor.
Make Extra Crumble: If you love the crumble topping, make a little extra to add on top.
Experiment with Flavors: Try adding different spices or extracts to change up the flavor.