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

In a large bowl, whisk together the unsweetened cocoa powder, all-purpose flour, baking powder, and salt until well combined.

In another bowl, beat the melted butter, eggs, vanilla extract, and granulated sugars until the mixture is smooth and glossy.

Gradually fold the wet ingredients into the dry mixture to create a rich brownie batter.

Using a cookie scoop or two spoons, drop rounded spoonfuls onto the prepared baking sheets, spacing them 2 inches apart.

Bake for 15-20 minutes, until edges are set and centers remain slightly soft. Cool on baking sheets for 10 minutes.

In a separate bowl, cream together softened butter, packed brown sugar, and granulated sugar until fluffy.

Mix in the vanilla, followed by flour and salt, then fold in chocolate chips.

Spread cookie dough filling on the flat side of one brownie cookie and top with another, pressing gently.

For a firmer filling, refrigerate the assembled cookies for about 30 minutes before serving.

Serve fresh with a cold glass of milk or your favorite ice cream.