Preheat the oven to 350°F (175°C).
Line a muffin tin with paper liners or grease it lightly.
In a large bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
In a separate bowl, mix the egg, milk, and vegetable oil together until combined.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fold in the chocolate chips gently.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack.
Enjoy your delicious double chocolate chip muffins!