Mix together plain flour, corn flour, baking soda and salt, sift it. Keep aside.
Beat butter, caster sugar and brown sugar in a bowl with electric mixer until light and fluffy. Add egg and vanilla extract, beat until combined.
Stir in sifted flour mixture. Add chocolate chips, mix well.
Drop level 1 1/2 tablespoons of mixture about 5 cm apart on baking paper lined oven trays. Press a few extra chocolate chips on top of each cookies, if desired. Cover the tray with a plastic wrap and chill for 2 hours.
Preheat oven at 160 °C for 10 minutes. Bake for 12 minutes or until light golden brown on the edges and still soft in the centre. Remove from oven and let the cookies cool completely on the tray.
Store cookies in a tightly sealed container for upto 5 days.
NOTE - One cup = 250 ml, one tablespoon - 15 ml, one teaspoon = 5 ml.
I used Hershey's semi-sweet chocolate chips in this recipe.