Preheat the oven to 350F. Grease a 9×9 baking dish with cooking spray and set aside. (I like this light metal pan.)
Cut the butter into tablespoon-sized pieces. Add the butter and chocolate chips to a large microwave-safe bowl. Microwave for 30 seconds. Stir well, microwave for another 15 seconds and then stir well again. Repeat for 15 seconds until chocolate and butter are completely melted and well-combined.
Add the granulated sugar and brown sugar to the butter mixture (you want it to be warm, even a little hot when you do this so the sugar dissolve) and whisk vigorously for 1 minute.
Stir in the eggs one at a time, whisking 20 seconds after each addition. Whisk in the vanilla extract, espresso powder and salt.
Using a rubber spatula, mix in the cocoa powder and gluten-free flour until fully combined. Stir in the chocolate chips.
Pour the batter into the prepared baking pan. Smooth into an even layer. Bake for 30-35 minutes until set and a toothpick inserted into the center of the brownies comes out clean.
Cool the brownies for 30 minutes before cutting. Slice and enjoy!