Preheat oven to 425°F. Line a 12-count muffin pan with cupcake liners and spray them lightly with baking nonstick spray. If you don't have liners, spray the muffin wells thoroughly.
To a large bowl, add the flour, sugar, cocoa powder, baking soda, baking powder, salt, espresso powder, and 1 ½ cups of the chocolate chips. Reserve the remaining ½ cup chocolate chips for topping. Whisk together and set aside.
In a second bowl, add the eggs, sour cream, vegetable oil, milk, and vanilla extract. Whisk until well combined.
Pour the wet ingredients into the dry ingredients and fold together using a silicone spatula. Avoid overmixing. The batter will be thick.
Scoop or spoon the batter into the muffin cups, filling them all the way to the top.
Top the muffins evenly with the reserved chocolate chips.
Bake for 5 minutes at 425°F, then, without opening the oven door, reduce the oven temperature to 350°F.
Bake for an additional 13 to 16 minutes, or until a toothpick inserted into the center comes out clean. Avoid overbaking.
Cool the muffins for 10 minutes in the pan, then transfer them to a wire cooling rack to finish cooling.