In a large mixing bowl, add sugar and sift together the self-raising flour, cocoa powder, baking powder, and salt. Whisk until well combined.
In a separate bowl, whisk the eggs, milk, vegetable oil, and vanilla extract until smooth.
Pour the dry ingredients into the wet ingredients and gently stir until just combined. Be careful not to over-mix, as this can make the muffins dense.
Gently fold in the roughly chopped dark chocolate chunks.
Spoon the batter into the prepared muffin cups, filling each about ¾ full. Sprinkle milk chocolate chunks on top of each muffin.
Bake in the preheated oven at 180°C (380°F) with a fan or 200°C (400°F) without a fan for about 15 minutes, or until a toothpick inserted into the center of a muffin comes out clean (or with a few moist crumbs).
Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Sift Dry Ingredients: Sift your dry ingredients, especially cocoa powder, to break up any lumps. This makes mixing easier and helps create a smooth, fluffy batter.Use Room Temperature Ingredients: Let eggs and milk come to room temperature first, it helps everything blend better for softer, lighter muffins.Gently Fold in Chocolate: When adding chocolate chunks, fold them in gently so you don’t over-mix. This keeps the chunks evenly spread in each muffin.Fill Muffin Cups Just Right: Fill each muffin cup about ¾ full. This gives the muffins room to rise without overflowing and helps them get a nice dome.Cool Muffins Properly: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. This keeps them from getting soggy on the bottom.Store for Freshness: Muffins are best fresh, but you can keep them in an airtight container at room temp for up to 3 days. Wrap individually for longer freshness or freeze up to a month.