In a separate bowl, combine the buttermilk, oil, eggs, and vanilla until well blended. With the mixer running on low speed, slowly pour the wet ingredients into the dry. Then, keeping the mixer running on low, pour in the coffee and mix gently, just until combined. Scrape the bottom of the bowl with a rubber spatula to ensure all ingredients are blended.
Into the bowl of a standing mixer fitted with the paddle attachment or a large mixing bowl, briskly whisk together the all purpose flour, whole wheat pastry flour, sugar, cocoa powder, espresso powder, baking soda, baking powder, and salt until well combined and no lumps remain.
Preheat the oven to 350 degrees F. Butter and lightly dust with cocoa powder a 6-cup bundt pan or a 8-inch x 2-inch round cake pan, tapping out the excess. If using a round cake pan, line the bottom with parchment paper, then butter and dush with cocoa again.