Preheat oven to 350°F / 175°C. Line the bottom and the sides of two 8" (20cm) baking pans with parchment paper. Set aside.
In a medium bowl combine flour, cocoa, sugar, baking powder, salt, and espresso powder and stir to combine. Set aside.
In a large mixing bowl with a stand or handheld mixer fitted with a whisk or paddle attachment, beat oil, eggs, buttermilk, and vanilla* just until combined.
Stir in dry ingredients to combine. The batter will be very thick.
Slowly mix in hot water until combined. The batter will be very thin.
Divide batter into the two prepared baking pans equally. Bake for 20-25 minutes or until a toothpick in the center comes out clean. Don't overbake. I baked mine for 22 minutes. Let cool in the pan for about 15-20 minutes. Then remove from pan and transfer to a cooling rack. Let cool to room temperature.