Preheat the oven to 325 degrees F.
In a mixing bowl, mix together flour, cocoa powder, and espresso powder. Set aside.
In the bowl of a stand mixer with the paddle attachment, add butter and sour cream and cream together for 3-5 minutes on medium speed, until mixed together. (may appear separated, this is normal)
Add vanilla extract, salt, and sugar and continue to mix for another minute. Add eggs, one at a time. Scrape down the sides of the bowl to ensure everything is mixed together and mix for another minute.
Add ½ of the dry ingredients, mix together, then add the remainder of the dry ingredients and mix until fully combined.
Spray a 10 cup bundt pan with nonstick baking spray and add batter. Bake for 1 hour and 20 minutes. Note: If using loaf pans, split batter between 2 9x5 loaf pans and bake for 50-60 minutes, until toothpick comes out clean. Allow cake to cool for 5 minutes in the pan then turn over onto a cooling rack or plate and allow to cool for 20 minutes.
To make the glaze, mix together milk, powdered sugar, and pb2 until smooth.