Preheat oven to 350°. Line three 9-inch round cake pans with parchment circles and spray with non-stick cooking spray. Set aside. In large bowl, sift together dry ingredients. Add eggs, buttermilk, oil and vanilla to dry ingredients. Beat mixture until combined and smooth (about 1 minute). Stir espresso powder into hot water (or make extra strong instant coffee). Add to batter and mix just until combined. Pour batter into pans and bake for 17-20 minutes, or until skewer comes out clean. Let cool 10 minutes, then remove cakes to wire racks to finish cooling.