Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9 x 5-inch loaf pan, or line with parchment paper for easy release.
Prepare the Chocolate Mixture: In a small saucepan, heat the whole milk until warm but not boiling. Remove from heat and whisk in the unsweetened cocoa powder until smooth. Set aside to cool slightly.
Cream the Butter and Sugars: In a large mixing bowl, brown the softened butter, granulated sugar and cocoa powder until light and fluffy.
Add Eggs and Flavorings: Add the eggs one at a time and mix well after each addition. Then, mix in the sour cream and vanilla extract until well combined.
Combine Dry Ingredients: In a separate bowl, combine all the purpose flour, baking powder and salt. If using, dissolve the instant coffee or espresso granules in a tablespoon of hot water and add it to the flour mixture.
Mix Wet and Dry Ingredients: Add the dry ingredients to the wet ingredients a little at a time and mix until combined. Be careful not to overmix.
Pour Batter into Pan: Pour the batter into the prepared loaf pan and smooth with a spatula.
Bake: Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean with a few crumbs attached.
Cool: Allow the cake to cool in the pan for about 15 minutes before transferring it to a wire rack to cool completely.
Serve: Once cooled, you can dust the top of the cake with powdered sugar if desired, or drizzle with chocolate ganache for extra decadence.
Enjoy: Slice and enjoy your delicious homemade chocolate pound cake with a cup of coffee or a glass of milk.