Start by placing the flour in a bowl.
Add the brown and white sugar and mix.
Add the cornstarch and mix again.
Add the butter and mix well.
Put the dough in a mixer or knead it well with your hands until the butter is incorporated with the rest of the ingredients and forms a kind of sand.
Add the egg and the egg yolk, the vanilla essence, and mix everything together. If necessary beat everything in the mixer to obtain a homogeneous mixture.
Add the salt, baking powder, and choco chips.
Mix very well and with the help of an ice cream scoop, spread the dough balls on a baking tray leaving at least 2 cm between each one.
Bake the cookies in a pre heated oven at 170º, for 11 min or until golden brown.
Repeat the process with all the cookies until all the dough is left.
Let them cool a little and sprinkle some salt on top (it accentuates the chocolate flavor).