Preheat your oven to 350°F (180°C).

In a medium bowl, combine flour, cocoa powder, baking soda, and salt. Whisk until well combined.

In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes).

Beat in the egg and vanilla extract until fully incorporated.

Gradually add the dry ingredient mixture to the wet ingredients, mixing until just combined.

Gently fold in the crushed Oreos until evenly distributed in the dough.

Using a cookie scoop, portion out the dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes or until the edges are firm but the centers are still soft.

Let the cookies cool on the baking sheet for a few minutes, then transfer them to a wire rack to cool completely.

Frost each cookie with buttercream once cooled.

Enjoy the richness of your freshly baked cookies!