Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking pan or line it with parchment paper.
In a large mixing bowl, combine the melted butter and granulated sugar. Stir until well combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, Ghirardelli cocoa powder, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
Fold in the Ghirardelli semi-sweet chocolate chips and white chocolate chips evenly.
Pour the batter into the prepared baking pan and spread it evenly with a spatula.
Bake for 22 to 25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Remove from the oven and allow to cool completely in the pan on a wire rack.
Once cooled, cut into 16 bars and serve.