Mix together plain flour, corn flour, baking soda and salt, sift it and Keep aside.
Beat butter, brown sugar and caster sugar in a bowl with electric mixer until light and fluffy. Add egg and vanilla extract, beat until combined. Stir in sifted flour, corn flour, baking soda and salt mixture. Add chocolate chips, mix well.
Cover the bowl with a plastic wrap and chill for at least 2 hours but not more than 12 hours. Let the dough sit at room temperature just until it is soft enough to scoop.
Preheat oven at 160 °C for 10 minutes. 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. 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 cookies cool completely on the tray.
Store the cookies in an airtight container for upto 4 days.
NOTE - I used Hershey's semi-sweet chocolate chips in this recipe.
One cup = 250 ml, one tablespoon = 15 ml, one teaspoon = 5 ml.