Preheat the oven to 425°. Line a 12 tin muffin pan with paper liners.
In a large bowl or stand mixer, combine flour, cocoa powder, baking soda, baking powder, and salt.
In another bowl, combine the espresso, milk, sugar ,eggs, and vanilla. Once eggs are fully incorporated, slowly pour in the slightly cooled melted butter.
Slowly add the wet ingredients to the dry ingredient bowl, using a wooden spoon or rubber spatula to carefully fold ingredients together. Be careful not to over-mix.
Once the batter is pretty well combined and no longer streaky, fold in the chocolate chips.
Use a large spoon or ice cream scoop to scoop about 3-4 tbsp of batter into each paper liner. Top each muffin with a few additional chocolate chips.
Place the muffin tin in the oven for 5 minutes, then reduce the temperature to 350, and continue to cook another 10-13 minutes, or until a toothpick comes out of the center of a muffin clean (melted chocolate chips don't count!)
Once done, remove from the oven and allow to cool for 5 minutes before transferring to a cooling rack.
Dust with powdered sugar and serve immediately or allow to cool to room temperature before enjoying!