Mix melted and cooled butter with granulated sugar
Add egg and vanilla extract to the butter mixture
Combine plain flour, cornflour, bicarbonate of soda, baking powder, and salt in a separate bowl
Mix dry ingredients into wet ingredients
Fold in 6 broken Oreos into the cookie dough
Divide dough into 8 portions and bake until soft and doughy
For the frosting, beat softened butter and room temperature cream cheese together
Add icing sugar and vanilla extract to the butter and cream cheese mixture
Fold in 3 broken Oreos into the frosting
Top cooled cookies with cream cheese frosting
Store in the fridge and bring to room temperature before eating, or store at room temperature and pipe frosting when ready to eat
