Sift all together all purpose flour, corn starch, baking soda and salt into one bowl. Set aside.
Melt your unsalted butter, and let it turn into brown colour and stir it well while browning. This could add rich caramel flavour to you cookies. Or you could just simply melt your butter without turn it into brown for simpler way.
Into your melted butter, add sugar, palm sugar, vanilla essence, and instant coffee which already dissolved with 2 tbs hot water. Stir them until all well combine and sugar dissolve and looks like caramel. Add whole egg and egg yolk one at a time, stir them well.
Add dry ingredient into the wet ingredient 1/3 at a time, stir them well using wooden spatula to make it easier. Add the chunks of 70% of dark chocolate and the chocolate chips. Stir them until all incorporate.
Scoop the chocolate chips cookie dough and place them into container (I used around 4 cm ice cream scooper). Chill the cookie dough in the fridge for at least 3 hours, or you could keep the rest of the dough up to 3 months in the freezer. (I only rest the dough that I'm about to bake into a freezer around 10 to 15 minutes, just to make it a bit firm before I bake it.)
Take some of your cookie dough out of your fridge, and thaw it for a while about 3 to 5 minutes just enough to make it easier to press.
Arrange your cookie dough over the baking paper, give some space in between, and push the dough a bit with your fingers and add the rest of chocolate chips on top and push the chocolate chip half in to make it stick finely over the dough.
Bake your cookie dough into a preheated oven at 180C around 10 minutes or depends on your oven. (I used small electric oven, and my oven a bit hotter than the common one, so I only used 150C and bake it around 10 minutes and sometime less than 10 minutes).
After 10 minutes, take out your cookies from the oven, and let it cool down on the tray around 5 minutes and move it on the cooling wire afterward to let it cool completely.
Serve perfectly with milk or coffee
