Preheat the oven to 350°F (175°C).
Grease a 9x13 inch baking pan.
Melt the butter in a saucepan over low heat.
Stir in granulated sugar and brown sugar until combined.
Remove from heat and let cool slightly; then stir in eggs and vanilla.
In a separate bowl, whisk together flour, cocoa powder, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Fold in the chocolate chips.
Pour the batter into the prepared pan and spread evenly.
Bake for 25-30 minutes, until a toothpick comes out with a few moist crumbs.
Let cool in the pan for 10-15 minutes before transferring to a wire rack.
Cut into squares and serve, optionally topped with nuts or caramel.
