Line muffin pan: Line a muffin pan with 12 paper liners. See note 4
Preheat oven: Preheat the oven to 370°F (190°C) 170°C (fan).
Dry ingredients: Sift all dry ingredients (flour, baking powder, baking soda, salt and sugar) in a bowl and mix together with a whisk or fork.
Wet ingredients: In a separate bowl, add all wet ingredients (buttermilk, melted butter, oil, milk, and vanilla extract) mix with a whisk or fork until combined.
Combine wet and dry ingredients: Pour the wet ingredient mixture into the bowl of the sifted dry ingredients.
Form a batter: Form a batter by mixing with a whisk or fork until just combined. Don’t over mix. See note 5
Fold in chocolate: Add the chocolate chunks and chocolate chips to the batter and use a spatula to gently fold it in.
Fill muffin cases: Spoon the mixture into muffin pans, filling each about ¾ full.
Sprinkle a few chocolate chips over the unbaked muffins (optional)
Bake: Bake in a preheated oven of 350°F° (180°C) for 15-20 minutes until baked and golden brown.
Remove baked muffins from the pan and cool on a wire rack.