1. Preheat the oven to 350°F and line two baking sheets with parchment paper.

2. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.

3. In a large bowl, beat the butter, brown sugar, and granulated sugar until light and fluffy.

4. Add the eggs and vanilla extract, then mix until smooth. Stir in the milk.

5. Gradually add the dry ingredients to the wet ingredients and mix just until combined. Fold in the chocolate chips.

6. Scoop the dough into even portions onto the prepared baking sheets, spacing them apart.

7. Bake for 9 to 11 minutes, then let the cookies cool on the pan for 5 minutes before transferring them to a wire rack to cool completely.

8. To make the filling, beat the cream cheese and butter until smooth. Add the powdered sugar, vanilla extract, and milk, then beat until fluffy.

9. Match the cooled cookies in pairs by size. Spread or pipe the filling onto the flat side of one cookie, then top with another cookie.

10. Chill for 15 to 20 minutes if you want the filling to set more firmly before serving.