Cut butter into 1 inch slices and melt in a medium saucepan over medium heat. Remove from heat and pour into the bowl of a stand mixer. Allow the butter to cool (for 30 minutes) while you prepare the dry ingredients. Alternatively, you can melt the butter in the microwave in 30 second intervals.
1 (227 g) cup Unsalted butter
In a medium bowl, shift together the flour, baking soda, cornstarch, and cream of tartar. Whisk in the kosher salt.
2 ¾ (344 g) cup All purpose flour , 1 teaspoon Baking soda , 1 teaspoon Cornstarch , ½ teaspoon Cream of tartar , ¾ teaspoon Kosher salt
In the stand mixer bowl with the melted butter, beat the melted butter and both sugars with the paddle attachment on medium high until the mixture is thick, creamy, and resembles a paste like consistency. About 2 minutes. Stop and scrape the sides and bottom of the bowl after 1 minute.
1 (200 g) cup Granulated sugar , ½ (110 g) cup Light brown sugar
With the mixer on medium speed, add in the eggs one at a time mixing until fully combined. Add in the vanilla extract with the last egg.
2 large Eggs, 1 tablespoon Vanilla extract
With the mixer on low speed, add the flour mixture in 3 additions, mixing until just combined. After adding the last of the flour mixture, mix until you only see a few streaks. Remove the mixing bowl from the stand mixer and add in the crushed Oreos, Oreo crumbs, and sprinkles. Using a rubber spatula, fold everything together until just combined. Cover bowl with plastic wrap and refrigerate for 3 hours. (While the cookies chill in the refrigerator, make the birthday cake crumble.) RECIPE BELOW
8 Golden Oreos , ¼ cup Golden Oreo crumbs , ⅔ cup All natural rainbow jimmies sprinkles
Line a plate with wax paper and set aside. Remove the chilled dough from the fridge and using a large cookie scoop, measure out 2.5 oz of dough per cookie. Lightly roll the dough into balls using the palms of your hands, they do not have to be perfect. Smooth out any cracks. Place the dough balls on the wax paper lined plate and place in the fridge uncovered to firm up, about 20 while the oven preheats.
Line a large cookie sheet with parchment paper and set aside. Preheat the oven to 350 degrees F. Place 5 balls of dough onto the prepared baking sheet, about two inches apart. Leave the remaining dough balls in the fridge until ready to bake.
Bake the cookies for 12 – 14 minutes. Remove the cookies from the oven halfway through baking and firmly tap the baking sheet on a heatproof surface to deflate the cookies. Rotate the baking sheet and return cookies to the oven and continue to bake.
Remove the cookies from the oven and using a small bowl or biscuit cutter, scoot the cookies in a circular motion until perfectly round. Top the cookies with birthday cake crumble, pressing down lightly so the topping adheres to the cookies. Allow cookies to cool on the baking sheet for 5 minutes then carefully transfer to a cooling rack to cool completely. While the cookies are cooling, make the vanilla glaze .