Preheat oven to 350 degrees Spray an 8-inch square pan with cooking spray.
Add melted butter, sugar, eggs, and vanilla to a medium bowl. Mix until combined.
Beat in cocoa powder, flour, salt, espresso powder, and baking powder. Mix until fully incorporated.
Add chocolate chips, and fold in until just combined.
Spread batter into the prepared pan, and bake for 20-25 minutes, or until just set.
Let cool.