Preheat the oven to 200C and line 6 muffin pan with paper baking cups
In a medium mixing bowl, combine the sugar and egg, whisk for about 3 minutes until fluffy and pale in colour. I use an electric hand mixer.
Add melted butter and oil into the egg mixture, whisk to combine.
Add yogurt, milk and vanilla extract, whisk to combine.
Sift in flour, baking powder, baking soda and salt. Fold gently until almost mix but not completely. You should still see some streaks of flour.
Toss in mini chocolate chips and fold gently to fully combine. Do not overmix. Stop folding once all the flour is fully incorporated. It is ok if the batter look slightly lumpy.
Scoop batter into prepared muffin pans, filling the cups full. Don't worry, the batter will not overflow in the oven.
Sprinkle mini chocolate chips on top of each muffins evenly. Use up all 20g of chocolate chips on 6 muffins. They may look crowded now but will be ok once the muffins puff up during baking.
Bake for 5 minutes at 200C, then lower the temperature to 180C and bake for a further 15 minutes. Remove from oven and allow to cool before eating.