Preheat oven to 350°F (175°C) and line muffin tray with liners.
In a bowl, mix flour, cocoa powder, baking powder, and salt.
In another bowl, whisk sugar, eggs, milk, and melted butter together.
Gradually add wet ingredients to dry ingredients, mixing until just combined.
Fold in chocolate chips or chunks for an extra gooey texture.
Spoon batter into muffin cups, filling each about 2/3 full.
Bake for 18-20 minutes, checking doneness with a toothpick test.