Prep Butter: Soften the butter to room temperature for easy mixing.
Mix Wet Ingredients: Whisk together softened butter and brown sugar until creamy. Add egg yolk and vanilla, then mix until smooth.
Add Dry Ingredients: Sift in cocoa powder, baking powder, all-purpose flour, and a pinch of salt. Combine into a dough.
Fold in Chocolate Chips: Gently incorporate the chocolate chips for bursts of flavor.
Shape Dough: Form a cookie shape and place it on a baking tray lined with parchment paper.
Bake: Bake at 180°C (350°F) for 11 minutes.
Cool & Enjoy: Let the cookie cool for about 10 minutes to set before devouring.