Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone baking mat.

1. In a large mixing bowl, beat together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.
2. Add the egg and vanilla extract, mixing until fully incorporated.
3. In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt.
4. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
5. Chill the dough for about 30 minutes if it’s too soft to handle.
6. Scoop about 1 tablespoon of dough, roll it into a ball, and place it onto the prepared baking sheet, spacing them about 2 inches apart. Gently press the dough balls down to flatten slightly.
7. Bake for 8-10 minutes, or until the edges are set and slightly golden. Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
8. To make the frosting, beat together softened butter and powdered sugar until light and fluffy. Add Oreo crumbs, vanilla extract, and heavy cream to achieve a smooth and creamy consistency.
9. Once the cookies are cooled, spread a generous amount of Oreo frosting on the bottom side of one cookie, then sandwich with another cookie. Press gently to spread the frosting evenly.
10. Serve and enjoy!