Preheat oven to 325, spray pan with non-stick spray or butter it and dust with cocoa powder.
Whisk flour, cocoa, espresso powder, salt and baking soda together & set aside.
Whisk buttermilk and sour cream together & set aside.
Beat butter and sugar together for about 5 minutes until very pale and fluffy.
Add eggs, one at a time, then add vanilla.
On low speed, add 1/2 of the flour mixture, then milk mixture, then the rest of the flour mixture. DO NOT OVERMIX!
Fill the bundt pan and smooth the top just a bit.
Bake for 45-60 minutes, until a cake tester comes out clean.
Cool cake completely before glazing.