Preheat oven to 350°F (175°C). Grease and flour a 9-inch round pan.
In a large bowl, combine flour, cocoa powder, sugar, baking powder, baking soda, salt, and espresso powder.
In a separate bowl, whisk milk, oil, eggs, and vanilla until smooth.
Gradually add the wet ingredients to the dry ingredients, mixing until combined.
Slowly add the boiling water, mixing until the batter is smooth (it will be thin).
Fold in the dark chocolate chips.
Pour the batter into the prepared pan and bake for 35 minutes or until a toothpick comes out clean.
Cool in the pan for 10 minutes before transferring to a wire rack.