Place a rack in the lower third of your oven and preheat the oven to 325 degrees F. Line the bottom and sides of an 8×8-inch baking pan with parchment paper and set aside. DO NOT use a 9x9 inch pan or your brownies will be thin and overcook.
Place the butter, granulated sugar, powdered sugar, cocoa powder, espresso powder, and salt in a medium heat proof bowl set over a pan of simmering water.
Stir periodically until the butter is melted and the mixture is evenly incorporated. It will be thick and gritty. Remove the bowl from the saucepan and set aside to cool, until it is just warm.
Add the water, vanilla, and first egg. Stir until the egg is fully incorporated. Then add the second egg and stir until it is fully incorporated. Continue stirring until the batter looks shiny.
Sprinkle the all-purpose flour and whole wheat flour over the top and stir until combined.
Once the flour has disappeared, stir the batter for 40 rotations (strokes). Stir in chocolate chips or any other desired mix-ins.
Transfer the batter to the prepared pan, smooth it into an even layer, then bake until a toothpick inserted in the center comes out mostly clean with just a few crumbs clinging to it, 25 to 30 minutes.
Let brownies cool completely in the pan on a wire rack. (I recommend cooling for at least 2 hours if you can stand it. They taste even better!). Using the parchment paper “handles”, gently lift the brownies onto a cutting board. Slice into squares and enjoy.
Notes
*Butter will yield brownies with the richest flavor and is tied for my top pick with olive oil. For dairy-free brownies, you can use canola oil for a taste that is the most similar to a boxed mix, or make olive oil brownies, which is my other favorite way to make this recipe. You can taste the olive oil; I love it as a pairing with chocolate, but for a more neutral flavor, use butter or canola oil.
TO STORE. Store leftover brownies in an airtight storage container in the refrigerator for up to 4 days.
TO SERVE. I enjoyed my brownies best either right out of the refrigerator or warmed in the microwave for a few seconds.
TO FREEZE. Freeze brownies in an airtight freezer-safe storage container for up to 2 months.