Preheat oven to 325 degrees. Lightly spray a 8x8 inch baking pan with non stick baking spray and line with parchment paper. Set aside. Read the back of the box mix and get the required ingredients ready such as eggs, oil, water, etc. Remember to swap out brewed coffee for water if the box mix calls for water.
Pour both packages of brownie mix into a large mixing bowl, add in the ingredients plus espresso powder (if you don't have brewed coffee) and vanilla extract. Mix to combine. Do not over mix brownie batter. If adding mix-ins to the batter fold them in to the batter. Pour brownie batter into the baking dish.
Bake brownies for 35-45 minutes. Test after 35 minutes with a tester. If tester comes out with a lot of brownie batter continue to bake brownies a little longer. If tester comes out with a little bit of brownie batter, remove brownies from oven and allow to cool. Allow brownies to cool for at least 30 minutes to give them time to set. Remove brownies from the pan by lifting up the sides of parchment paper. Cut into squares and serve. eftovers can be stored in an airtight container.