Preheat the oven to 425 degrees. Prepare 2 muffinn tins with 14 paper liners.
In a medium microwave safe bowl, melt the chocolate in the microwave in 30 second intervals, stirring after each one until completely melted. Let the chocolate cool for at least 10 minutes.
In a medium bowl, combine the flour, cocoa powder,brown and white sugar, baking soda, baking powder, salt and espresso powder.
Once the chocolate has cooled, whisk in the eggs, oil and sour cream until combined.
Add the flour mixture to the wet ingredients, stirring until almost all of the flour is stirred in.
Add the chocolate chips and stir until they are just evenly combined and avoid overmixing.
Divide the mix between the muffin cups, filling to the top. Top with additional chocolate chips if desired.
Bake the muffins for 5 minutes at 425 degrees and then turn down the temperature to 350 and continue to bake for 11-12 minutes more until a toothpick inserted into the middle comes out clean.
Let cool for a couple minutes in the pan before enjoying!