Line a muffin baking tin with muffin liners. Either a 6-hole muffin tin for jumbo muffins, or a 12 hole cupcake tin for regular-sized muffins.
In a large bowl, stir the flour, sugar, and baking powder together to combine. Make a well in the middle and set aside for now.
300 grams Self-raising flour, 200 grams Caster sugar, 1 teaspoon Baking powder
In a separate bowl, whisk the oil, eggs, milk, buttermilk, and vanilla extract together.
100 millilitres Vegetable oil, 2 medium Eggs, 120 millilitres Whole milk, 100 grams Buttermilk, 2 teaspoons Vanilla extract
Pour the wet ingredients into the dry and gently mix until just combined. Be extra careful not to overmix at this stage, a lumpy mixture with lots of air bubbles is what you're looking for.
Fold in the chocolate chips (save a handful for later). OPTIONAL: Cover the bowl with clingfilm and let the mixture rest at room temperature for 30 minutes. This will give your muffins a better rise!
200 grams Chocolate chips
Preheat the oven to 200°C fan / 220°C conventional.
Divide the mixture evenly between the liners filling each one to the top. Sprinkle some extra chocolate chips over each.
Bake for 10 minutes. Then, with the oven door closed, reduce the temperature to 180°C fan / 200°C fan and bake for a further 15 minutes. The muffins should rise tall, turn golden brown, and spring back lightly when pressed.
Allow to cool for 5 minutes in the tin, then lift out and transfer to a wire rack to continue cooling.
These muffins are best served warm and fresh, or store in a baking tin and enjoy within 4-5 days.