Preheat oven to 220°C.
Spray a 12 cup muffin tray with non-stick cooking spray or line with paper liners.
Make buttermilk: Stir the milk and lemon juice together in a measuring cup. Let the mixture stand at room temperature for 5 to 10 minutes. Once it’s ready, the milk will be slightly thickened and you will see small curdled bits.
In a large bowl, whisk together the flour, baking powder, baking soda, salt and chocolate chips. Set aside.
In a medium bowl, whisk together the melted butter, sugar, eggs, milk mix, and vanilla essence
Slowly add the wet to the dry ingredients, and gently fold together until just combined. Remember not to over mix at this point.
Divide the batter into the 12 muffin cups and bake at 220°C for 5 minutes. Then reduce the oven temperature to 190°C and continue to bake for another 10-12 minutes or until a toothpick inserted into the center comes out clean.
Let cool for about 5-10 minutes and enjoy warm.