Based on: https://lifestyleofafoodie.com/how-to-make-boxed-brownies-better/
Follow the box instructions, except: substitute milk for water, butter for oil; add vanilla extract, salt, espresso grounds, and chocolate chips.
1. Preheat oven to 325F.
2. Mix wet ingredients (milk, butter, egg, vanilla extract) in a bowl.
3. Add dry ingredients (brownie mix, espresso grounds, salt, walnuts, and chocolate chips). Stir until just blended.
4. Sprinkle sea salt on top.
5. Bake for 40 minutes, or until a toothpick comes out clean.