Preheat oven to 200C/390F (all ovens) (Note 6). Line a 12 hole muffin tin with paper patties.
Whisk flour, baking powder, baking soda, sugar and salt in a bowl. Stir through chocolate chips.
In a separate bowl, whisk buttermilk, melted butter, oil, eggs and vanilla.
Make a well in the flour bowl, pour in egg mixture. Mix until just combine - try not to stir more than 8 times. Some flour lumps in the batter is fine.
Divide batter between paper cases. Top with remaining ¼ cup chocolate chips.
Bake for 5 minutes, then turn down to 180C/350F (fan forced/convection) and bake for a further 15 minutes, or until a skewer inserted into the muffin comes out clean.
Remove muffins from the muffin tin immediately onto a cooling rack.
Serve warm or at room temperature (warm is extra yum!)
