Preheat the oven: Preheat your oven to 350°F (175°C) and line or grease your muffin tin.
Prepare the dry ingredients: In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
Mix the wet ingredients: In a separate bowl, whisk together the sugar, eggs, milk, vegetable oil, and vanilla extract until smooth.
Combine wet and dry ingredients: Slowly add the wet mixture to the dry ingredients and stir until just combined. Be careful not to overmix.
Add chocolate chips: Gently fold in the chocolate chips, making sure they are evenly distributed.
Fill the muffin tin: Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.
Bake: Place the tin in the oven and bake for 18-20 minutes, or until a toothpick inserted into the centre comes out clean.
Cool: Let the muffins cool in the tin for 5 minutes, then transfer them to a cooling rack to cool completely.