Add the butter and sugar to a large bowl and mix for around a minute until it forms little nuggets. You don’t want to cream the mixture together.
Add in the chocolate chips, plain flour, bicarbonate of soda, corn flour and mix again until the chocolate chips are evenly disturbed.
Finally add in the egg and vanilla extract and mix again until a dough is formed.
Roll the dough into balls around 100g-125g. Flatten each ball out and add in a crème egg. Completely cover the crème egg with the cookie dough and place them in a freezer safe container or baking tray lined with baking parchment.
Put the cookie dough balls into the freezer for 45 minutes.
Just before you remove the cookie balls from the freezer preheat the oven to 180C (160C Fan) and line two baking trays with baking parchment.
Place the cookie dough balls onto the baking trays. Make sure they are spaced apart as they will flatten and spread in the oven and you don’t want them to touch.
Bake in the oven for 14-16 minutes.
Leave the cookies to cool fully on the baking tray. They will be quite soft when you first take them out the oven but will firm up as the cool.