Preheat the oven to 350°F (175°C) and grease a baking pan.
In a large bowl, melt the butter and stir in the sugar.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the chocolate chips.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Let cool in the pan before cutting into squares.