Preheat oven to 350 degrees and line a cupcake tin with liners. In a bowl, whisk together the flour, baking powder, cocoa powder and salt and set aside. In the bowl of a stand mixer fitted with the paddle attachment, or a separate bowl using a hand mixer, beat the butter and both sugars together on medium-high speed until light and fluffy, about 2 minutes. Add your eggs, one at a time, beating well in between each addition. On low speed, add half of your flour mixture and mix until combined. Add the buttermilk and mix until combined. Fold in the other half of your dry ingredients and then add the smashed Oreos and mix until just combined. Do not over-mix! Divide the batter evenly between the lines and bake for 18-20 minutes or until a toothpick comes out clean.
Frosting
Beat your room temperature butter for about 2 minutes until creamy. Add in the powdered sugar and beat until combined. Add in the Oreo crumbs (which you can get by running Oreos through a blender/food processor, or by putting them in a ziplock bag and hitting it with a wooden spoon) and mix until incorporated. Mix in the heavy cream until fully combined. Once your cupcakes are completely cool, frost and enjoy!