Prepare the Pound Cake: Preheat the oven to 325°F (165°C) and line a 9×5-inch loaf pan with parchment paper.
In a medium bowl, whisk together the flour, Dutch process cocoa powder, black cocoa powder, espresso powder (if using), baking powder, and kosher salt.
In the bowl of a stand mixer fitted with the paddle attachment, beat the room-temperature butter and granulated sugar together on medium speed for 2-3 minutes, or until light and fluffy.
Add the vanilla extract, then the eggs one at a time, making sure to fully incorporate each egg before adding the next.
Scrape down the sides of the bowl, then add half of the dry ingredients. Mix on low speed until combined, then mix in the sour cream. Add the remaining dry ingredients and mix until fully incorporated, being careful not to overmix.
Bake: Pour the batter into the prepared loaf pan. Tap the pan on the counter a few times to release any air bubbles. Bake for about 1 hour and 20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the pound cake to cool completely in the pan before transferring it to a wire rack.
Make the Chocolate Glaze: In a small saucepan, heat the heavy cream over medium heat until it reaches a simmer (about 190°F). Remove from the heat and add the chopped chocolate. Stir gently until the chocolate has melted and the mixture is smooth.
Finish the Cake: Pour the chocolate glaze over the cooled pound cake, letting it drizzle down the sides. Allow the glaze to set for a few minutes before slicing and serving.