Preheat your oven to 350°F (175°C). Grease and line a 9x13 inch baking pan with parchment paper.

In a large mixing bowl, combine the granulated sugar, brown sugar, and melted butter. Whisk until smooth and well combined.

Add the eggs one at a time, mixing well after each addition. Then stir in the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder.

Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Do not overmix. Fold in the chocolate chips.

Pour the brownie batter into the prepared baking pan, spreading it evenly.

If using, drop dollops of peanut butter on top of the brownie batter. Use a knife or toothpick to swirl the peanut butter into the brownies.

Bake for about 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan for about 10 minutes before lifting them out using the parchment paper. Transfer to a wire rack to cool completely before cutting into squares.

For added richness, consider adding more chocolate chips on top before baking.

Store the brownies in an airtight container at room temperature for up to 5 days or freeze for longer storage.