• Preheat the oven to 350°F. Line 3 baking sheets with parchment paper and set aside.
• In the bowl of a stand mixer fitted with the paddle attachment, cream the softened butter and the sugar until smooth and fluffy, scraping down the sides of the bowl as needed.
• Add the vanilla and the eggs. Mix until fully combined.
• Add the flour, the baking powder, and the salt. Mix until the dough comes together, scraping down the sides of the bowl often so everything is evenly incorporated.
• Fold in the crushed Oreos until evenly distributed throughout the dough.
• Using a large ice cream scoop, portion the dough onto the prepared baking sheets, spacing the cookies apart to allow for spreading.
• Bake for about 10 minutes, until the centers are set. Remove the cookies from the oven and let them cool completely on the baking sheets or transfer them carefully to a wire rack before decorating.

For the frosting

• Add the softened butter and about half of the powdered sugar to the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until combined.
• Add the milk, the salt, the vanilla, and the remaining powdered sugar. Mix on low speed until combined, then increase the speed to medium and beat until the frosting is smooth and creamy, scraping down the sides of the bowl as needed.
• Fold in the crushed Oreo pieces until evenly distributed throughout the frosting.
• Once the cookies are completely cool, spread a thin layer of frosting over the top of each cookie.
• Top each cookie with 1 mini Oreo for decoration.