Preheat oven to 350 degrees, then prepare 8x8 baking pan by cutting two pieces of parchment paper and crisscrossing them in the bottom and up the sides of the pan to form a sling.
Put butter, cocoa powder, chocolate chips and salt into a large microwave safe bowl. Microwave at 30 second intervals, whisking after each 30 seconds until mixture comes together.
Once everything has melted together, add the sugar and whisk well until the mixture gets glossy. Whisk in the vanilla and espresso powder, making sure everything is well incorporated.
Add the eggs one at a time, whisking well between additions and then until it is super glossy. This could take 2-3 minutes.
Mix the baking powder into the flour, then using the spatula, fold the flour in just until you can’t see it anymore.
Pour into the parchment lined pan and bake at 350 degrees for 30-40 minutes (depending on your oven).
Let cool in the pan for about 10 minutes and then lift out using the parchment paper sling. Let cool another 20 minutes, then place on cutting board, cut into squares and enjoy!
Notes
This recipe can easily be doubled and baked in a 9x13 baking pan. You will need to increase the cooking time by 10-15 minutes.These one bowl brownies freeze great! Once you slice them, wrap them well in plastic wrap and store in an air tight container in the freezer for up to 2 months.