Mix the hot water and coffee and keep on the side.
Mix the flour, cocoa powder and corn starch; keep on the side.
In a bigger bowl, mix the butter and sugar until combine. Add the egg yolk and the coffee to it and mix it.
At this point, add the flour, cocoa and cornstarch mixture and form the dough.
Wrap into a saran wrap and place into the fridge for a half of hour.
After was rested in the fridge for half of the hour; form the cookies by rolling small pieces of dough into a 3-4 cm oval shape (or any size you like, just adjust baking time) and place on a baking tray lined with parchment paper.
Using the back of a small knife, cut into the cookie dough, making it look like coffee beans.
Place cokes tray in the fridge or frizzier for five minutes.