Preheat oven to 350°F (177°C). Spray three 8-inch cake pans with nonstick cooking spray and line the bottom of each pan with parchment paper. Set aside.
In a large mixing bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Whisk in the granulated sugar and brown sugar until well combined. Then, add the oil, buttermilk, eggs, and vanilla extract and mix until just combined.
Add the instant espresso powder to the cup of boiling water and mix until fully dissolved. Add to the mixing bowl and mix until everything is just combined. The batter will be thin.
Evenly distribute the batter between all three cake pans. Bake at 350°F (177°C) for 28-30 minutes or until a toothpick inserted into the center of the cakes comes out clean and the tops spring back when lightly touched.
Remove from the oven and transfer to a wire rack to cool completely.