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

In a bowl, whisk together cocoa powder, flour, baking soda, baking powder, and salt until well combined.

In a large bowl, cream together the granulated sugar, brown sugar, and softened butter using an electric mixer until light and fluffy.

Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the milk, mixing until just combined.

Drop spoonfuls of batter onto the prepared baking sheet, spaced a few inches apart.

Bake for 10-12 minutes or until the edges are set. Let the cookies cool completely on a wire rack.

For the filling, beat together the softened butter, powdered sugar, vanilla, and milk in a bowl until smooth and creamy.

Spread filling on the flat side of one cookie and top with another cookie, creating a sandwich.

Repeat with remaining layers.