Preheat the oven to 350°F. Line a 9x13 pan with parchment paper or lightly coat with nonstick spray.
In a saucepan, melt butter over low heat. Once the butter is melted, add sugars and stir to combine, continuing to heat and stir until sugar is heated through but not bubbling.
Pour mixture into a large bowl, then stir in cocoa powder, salt, baking powder, coffee extract (if using), and vanilla extract. Add eggs and stir until smooth.
Stir in flour, peppermint chips, and chocolate chips, mixing until smooth and no white bits remain.
Pour batter into prepared pan and bake for 30 minutes. Let cool completely before cutting.