CRUMB TOPPING: In a medium bowl, use a fork to cut together the softened butter, sugars, salt, graham cracker crumbs and flour. Mixture will be crumbly. Place crumb mixture in the refrigerator while you prepare the cookie dough.

COOKIE DOUGH: In the bowl of a stand mixer, affixed with the paddle attachment on medium-high speed, add the butter, white sugar and brown sugar. Mix until creamy. Add the egg and vanilla extract. Mix until combined. Change mixer to low speed and add the flour, cornstarch, baking powder, baking soda, salt and nutmeg. Mix until just combined.

Remove the bowl from the mixer and use a rubber scraper to ensure the cookie dough is well incorporated. Gently fold in the blueberries.

Use a standard cookie scoop to scoop cookie dough balls. Place a piece of parchment paper on a cookie sheet. Remove the crumb mixture from the refrigerator. Roll cookie dough balls in the crumb mixture and place on the cookie sheet. Gently flatten the tops of the cookie dough balls slightly and add remaining crumb mixture evenly to the tops of all the cookies. Place cookie sheet in the refrigerator to chill for at least 2-3 hours (I chilled mine overnight).

Once cookies have thoroughly chilled, preheat oven to 350-degrees. Bake cookies for 14-16 minutes or until the crumb topping is a light golden brown. Allow cookies to cool and set on the cookie sheet before transferring to a wire rack to cool completely.