Preheat oven to 180c/350F. Line a flat tray/cookie sheet with parchment/baking paper.
Place butter, brown sugar and white sugar into the bowl of the mixer or bowl for hand mixer and beat until light and creamy.
Add in egg and vanilla and beat till combined.
Add in flour, bicarb soda, salt and corn starch/flour and beat until it forms a dough.
Chop up Kinder bars into chip sized pieces.
Place chocolate chips and chopped bars into the dough and mix through with a spatula until the chocolate is dispersed throughout the dough.
Take heaped tablespoons of mixture and roll into balls.
Place onto prepared cookie sheet leaving about 3 inches between each cookie to allow for spreading. Place in the oven for 10-11 minutes.
Cookies are ready when the edges are starting to turn golden in colour and the centres are still soft. The cookies will continue to cook and set on the tray after baking so it's best to take them out before they are baked through.
Cool down completely before serving.