Preheat oven to 180°C.
Mix 310g all-purpose flour, 1 teaspoon baking powder, and 1 teaspoon baking soda in a bowl. Add 60g corn starch for extra crunch.
In another bowl, soften 250g salted butter at room temperature until still solid. Mix in 200g soft brown sugar, then beat in one large egg and 1 teaspoons vanilla extract. Beat well.
Gradually mix in the flour mixture into the wet ingredients.
Fold in 4 tablespoons vegetable oil, then stir thoroughly.
Add chocolate chips and mix to distribute evenly.
Chill dough for 1 hour in a refrigerator.
Form cookie dough into balls and place on a baking tray. Top with additional chocolate chips if desired.
Bake for 15-20 minutes at 180°C (top and bottom heat) until golden brown, depending on your oven's temperature.
Allow to cool for a few minutes before serving.