1. Preheat the oven to 180°C and grease a square mold.
2. In a bowl, mix the melted butter and sugar until the mixture is creamy.
3. Incorporate the eggs one by one, then add the vanilla extract.
4. In another bowl, mix together the cocoa powder, flour, salt and baking powder.
5. Incorporate the dry ingredients into the wet mixture until you obtain a homogeneous dough.
6. Pour the batter into the mold and bake for 20-25 minutes.
7. Let cool before cutting into squares.
