Recipe adapted from Nigella Lawson.
Preheat oven to 375°. Grease or line a 12-cup standard muffin pan.
Whisk together flour, baking powder, baking soda, cocoa, and sugar. Stir in 3/4 cup chocolate chips. Add milk, oil, egg, and vanilla, and stir just until blended.
Spoon batter into prepared pan. Sprinkle remaining 1/4 cup chocolate chips on top. Bake 20 minutes, or until muffins are dark, risen, and springy.