Preheat the oven to 350 degrees F (175 degrees C). Grease a baking tray with butter or oil and set aside.
Take the puff pastry sheets, cut them into small rectangles of equal sizes, and place them on the greased baking tray.
In a medium saucepan, mix together the butter, cornflour, and sugar. Then add the milk while stirring continuously on medium heat until thick and creamy.
In a separate bowl, beat two eggs and add to the mixture in the saucepan. Continue stirring until smooth.
Pour this mixture onto the puff pastry rectangles and let it cool.
In a separate bowl, combine the chocolate chips and beaten egg to make the dough for the tail of the Cheshire Cat.
Spread this mixture over each puff pastry rectangle and cut it into the desired shape.
Bake these rectangles in the preheated oven for 20 minutes or until they are golden brown.
Now make the icing for the tail by combining 6 tablespoons of milk and 1/2 cup of powdered sugar in a small bowl. Divide this mixture into two parts and add food colors to each part.
When the rectangles are baking, drizzle one half with the white icing and the other half with the colored icing.
Transfer them to a plate and serve immediately!