Prep: Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease with non-stick spray.
Dry Ingredients: In a large bowl, whisk together flour, cocoa powder, baking powder, and salt.
Wet Ingredients: In another bowl, mix the melted butter, sugar, eggs, milk, and vanilla extract until well combined.
Combine: Pour the wet ingredients into the dry ingredients. Stir until just combined. Fold in the chocolate chips.
Fill and Bake: Divide the batter evenly among the muffin cups, filling each about ¾ full. Sprinkle additional chocolate chips on top. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
