Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking pan.
Melt the butter in a medium saucepan over low heat.
Remove the saucepan from the heat and stir in the granulated sugar, mixing until smooth.
Add eggs, one at a time, and then mix in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Gently fold the dry ingredients into the wet mixture until just combined.
Stir in the chocolate chips.
Pour the batter into the prepared baking pan and smooth the top.
Drop spoonfuls of peanut butter on top and gently swirl with a knife.
Bake for 25-30 minutes or until a toothpick inserted comes out with a few moist crumbs.
Allow brownies to cool in the pan before cutting into squares.