Melt the cooking chocolate in a double boiler (fill a large vessel with water and then keep a small vessel inside which contains the chocolate to be melted. You can also use microwave to melt the chocolate but be careful not to burn it.
Dissolve the coffee powder in a little water to make a thick paste.
Proceed normally to make a regular custard. (Use the steps I have described above in the post if you have never made custard before using custard powder)
Now add the melted chocolate and coffee in the custard and boil for another 3-4 mins.
Remove from the stove and let it cool a little.
Crumble the mix cookies with hands and sprinkle on top of the custard after its a little cool. This has to be done when it has become lukewarm.. If it is too early means the cookies will become too soft and too late means they will not blend.
Let the custard set in the refrigerator for 4-5 hrs.