Preheat your oven to 350°F (175°C). Line a small baking pan with parchment paper.

Melt the unsalted butter in a small saucepan over low heat. Stir in the granulated and brown sugars until smooth and glossy.

Whisk in the egg and vanilla extract until fully incorporated.

Fold in the cocoa powder, all-purpose flour, salt, and baking powder gently.

Mix in the chopped chocolate or chocolate chips.

Bake in your preheated oven for 18–22 minutes until edges are set, but the center is still soft.

Cool completely in the pan before slicing into squares.