1. Have ingredients at room temperature. Place rack in lower third of oven; heat to 350 degrees F. Spray 12-cup Bundt or tube pan with nonstick spray.
2. Sift together flour, cocoa, baking soda, baking powder and salt. Set aside. Whisk whole eggs with whites in a small bowl. Set aside. Dissolve espresso powder in 3 tablespoons warm water and combine with vanilla and buttermilk in small bowl.
3. Cut butter into chunks and place in an electric mixer bowl. Using a stand mixer, beat to soften, about 1 minute. Add sugar gradually, beating constantly for about 3 minutes at medium speed. Gradually dribble in eggs, beating at medium-high speed for 2 to 3 minutes. On medium-low speed, beat in a third of the flour mixture, scraping bowl as necessary. On medium speed, gradually dribble in half of the buttermilk mixture, scraping the bowl. On low speed, beat in half of the remaining flour followed by the rest of buttermilk mixture, scraping bowl as necessary. Beat in remaining flour mixture until well combined. It is okay if batter looks slightly curdled.
4. Scrape batter into pan and smooth top. Bake at 350 degrees F for 50 to 55 minutes or until cake starts to shrink from the sides of the pan and toothpick inserted into center comes out barely clean. Do not overbake.
5. Cool on a wire rack for 10 minutes. Invert and remove from pan. Cool completely on rack before storing. Cake stays moist for 4 to 5 days, well wrapped; or freeze for up to 2 months.