Start by preheating your oven to (220°C / 425°F / gas mark 7)
In a large microwave safe bowl, melt the butter and add in the sugar and mix well.
Next, crack in the eggs and whisk together.
Pour in the buttermilk, sour cream, salt and vanilla. Whisk until everything is well mixed. (If you don't have buttermilk, simply mix 60ml (¼ cup) of milk with 2 tsp of lemon juice or vinegar and let it sit for around 10 minutes, before adding it into the egg mixture.)
Next, add in the flour and baking powder and fold till combined, but don’t overmix.
Coat the chocolate chips in 2 tbsp of flour and coat them really well, massage them a little longer than you think you need to, they should be covered in flour.
Add the chocolate chips into the muffin batter and fold gently.
Scoop the muffin batter into a lined muffin or cupcake tray, using a large ice cream scoop or a ½ cup measure. You should get 12 muffins.
Sprinkle on some granulated sugar and extra chocolate chips if desired.
Bake for 5 minutes at (220°C / 425°F / gas mark 7), then turn the oven down to (190°C / 375°F / gas mark 5) and bake for an additional 15 minutes, until muffins are golden brown and spring back to the touch. Remove from the oven and allow to cool for at least 15 minutes before eating!
Enjoy!