Make the flour mix by combining sifted flour, baking soda, cornstarch and salt in a large bowl.

In a separate medium sized bowl mix melted butter, brown sugar, and white sugar. Whisk these until all is blended and there are no chunks of brown sugar.

To the sugar mix, whisk in the vanilla paste, whole egg, and the extra egg yolk. The contents should be runny.

Combine the dry and wet ingredients, mix together with a large spoon or rubber spatula. Fold in the chocolate chips.

Cover the dough tightly and place in the fridge for 2-3 hours.

After this, take the cookie dough out of the fridge and allow it to soften to room temperature.

Preheat the oven to 160℃.

For medium/large cookies use two tablespoons of dough per cookie. Roll the dough into a tall ball.

Place the balls of cookie dough on a lined baking tray.

Bake for 12-14 minutes, until the outer edge of the cookies are slightly browned.

Place a few extra chocolate chips on top while the cookies are still hot, then leave to cool for 10 minutes.