Preheat oven to 350°F (177°C). Spray two 9-inch cake pans with nonstick cooking spray, line the bottom of each pan with parchment paper, and 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, 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 just combined (the batter will be very thin)
Evenly distribute the batter between both 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 in the pans for 30 minutes. Run a knife around the outside of each cake layer in the pan then carefully remove the cakes from the pans and place on the wire rack to cool completely.