Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until combined. In a large bowl, cream butter with granulated and brown sugars until light and fluffy, about 2-3 minutes. Add vanilla and eggs, mixing until incorporated. Gradually stir in dry ingredients until just combined.

Using a cookie scoop or tablespoon, drop approximately 1.5 tablespoons of dough onto the prepared sheet, leaving space between scoops. Bake for 10-12 minutes, until edges are firm but centers look slightly soft. Let them cool on a wire rack.

Once cooled, scoop 1 tablespoon of marshmallow fluff onto each cookie, spreading gently. Chill in the fridge for 15-20 minutes to set the fluff.

Melt half of the dark chocolate chips in a microwave-safe bowl in 20-second increments, stirring until smooth. Dip the tops of each cookie in the chocolate, coating the marshmallow fluff, and shake off excess.

Chill the dipped cookies in the refrigerator for 25-30 minutes to set the chocolate.