Preheat oven to 400 degrees F (205 degrees C).
Into a mixing bowl, add Self-Rising Flour (2 cup) and Caster Sugar (1 cup). Mix to combine.
Into a mixing jug, add Buttermilk (1 cup), Butter (80 gram), Vanilla Extract (1 teaspoon), and Egg (1). Whisk to combine. It might seem like it's starting to curdle, but that perfectly normal, it's just the butter solidifying.
Make a well in the center of the dry ingredients. Add Chocolate Chips (200 gram), reserving some to top the muffins later. Pour in the wet ingredients and mix well.
Transfer batter to a muffin tin lined with muffin wrappers. Scatter extra chocolate chips on top and press down lightly so they stick to the batter. Bake for 20 minutes.
Let muffins rest for 5 minutes in the pan, then transfer to a wire rack to cool completely or eat warm! Once cooled completely, these will keep for up to 3 months if frozen in a ziplock. Just zap in the microwave to thaw and warm.