Spray a 12 cup muffin tray with non-stick cooking spray or line with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, cocoa salt, and chocolate chips.
Set aside.
Combine the milk and the lemon juice. Let it stand for at least 5 minutes.
In a medium bowl, whisk together the melted butter, sugar, eggs, milk mix, and mint 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.