In a mixing bowl, mix together the flour, cornstarch, baking soda, vanilla and salt. Set aside.
In another bowl, whisk the oil with milk, instant coffee and sugar.
Pour wet to dry ingredients and mix until you have a sticky dough. Fold in 2 tbsp of the chopped chocolate. cover and refrigerate for 20 mins.
Preheat your oven to 180ºC and line a baking sheet with parchment paper.
Divide dough to 10 equal balls and flatten with your hand to desired thickness and decorate with the remaining chopped chocolate.
Bake in preheated oven for 10-12 mins, not more. Remove and leave the cookies to cool in the pan for another 10 mins.