Preheat the oven to 170 deg Fan assisted. Place 12 paper Muffin cases into a muffin tin.
Mix together the melted butter, egg, buttermilk, vanilla extract and whole milk into a suitably sized jug. Leave to one side while you deal with the dry ingredients.
115 g butter, 1 medium egg, 140 g Buttermilk, 1 teaspoon vanilla extract., 4 tablespoons milk
In a separate bowl, mix together the flour, sugar and baking powder along with the White, Dark and Milk chocolate chips.
255 g Plain Flour, 1 tablespoon baking powder, 170 g soft brown sugar, 50 g white chocolate chips, 100 grams milk chocolate chips, 50 grams dark chocolate chips
Pour the liquid mix into the flour and chocolate chip mixture, mix until well combined with no visible floury bits.
Using a large spoon or ice-cream scoop, place equal amounts of batter into the Muffin cases to about ¾ full allowing the muffins to rise a little. Do not overfill.
Bake in the oven for 20 - 25 mins, or until baked with a nice golden colour. Test the centre of the Muffins with a cake skewer until it comes out clean.
Take out of the oven and turn out onto a wire cake rack to cool completely.