Preheat your oven to 350°F. Line a 9x5-inch loaf pan with parchment paper leaving a 2-inch overhang along the long sides. Grease the exposed short sides with butter.
Whisk together sour cream, eggs, oil, vanilla and espresso powder in a medium bowl until smooth and evenly blended.
Sift flour, cocoa powder, baking powder and baking soda into a large bowl. Add granulated sugar, salt and chocolate chips and whisk to blend evenly.
Make a well in the center of the dry ingredients and pour in sour cream mixture. Gently stir until it starts to become absorbed, but a few streaks remain. Add milk and continue mixing until batter is evenly combined. Pour batter into prepared pan and smooth it out.
Bake for 45-55 minutes until a skewer inserted into the center comes out clean despite any remnants of melted chocolate chips.
Transfer pan to a wire rack and let cool for 10 minutes. Run a knife along the short sides to release the loaf, lift it out of the pan and transfer it onto the rack to cool completely.
To make the glaze, combine dark chocolate, honey or corn syrup and cream in a small saucepan over low heat and whisk gently until smooth and glossy. Let it cool for 10-15 minutes until it is thickened, then pour it over the loaf cake and let set for 20 minutes before slicing.