Preheat the oven to 370℉/180℃. Line two large baking trays.
In a bowl, use an electric mixer or stand mixer to whisk together your butter and both sugars until fully combined - it should look light and fluffy. Add egg and vanilla and mix again.
Add the flour, cocoa powder, baking powder, baking soda and Oreo crumbs and mix. It should form a thick cookie dough.
Scoop heaped tablespoons of the cookie dough and roll into balls and place on the baking trays, at least 2 inches apart. Press down lightly before baking for 9-10 minutes.
OPTIONAL: After baking but while still warm, to neaten the cookies into perfect circles you can use a large cookie cutter. Place the cookie cutter around the cookie (being careful not to cut any cookie), and spin the cookies round so they neaten.
Let cool on a wire rack.
Make the frosting by whisking the butter and cream cheese on a high speed until soft. Add in half the powdered sugar and mix to combine. Add the remaining powdered sugar and mix to form the frosting. Add in a teaspoon or so of milk or heavy cream if it feels too thick to spread.
Spread the frosting over the cookies and finish by sprinkling over more crushed Oreos.
