Crush cookies of your choice and keep it aside.Add cocoa powder, corn flour and ½ cup warm milk in a pan and mix it well. Make sure there are no lumps.Add remaining milk, sugar and cook it on low flame for 4-5 minutes or until the sauce thickens. Keep stirring.Cook and stir until the mixture thickens enough to coat the back of the spoon. Remove from the flame and add vanilla essence and mix it well and keep it aside and let it cool down completely.Now take a glass or bowl and add one layer of crushed cookies. Sprinkle some nuts on top of it. Next add a layer of pudding. Again add a layer of crushed cookies ans sprinkle some nuts on top of it. Add another layer of pudding and top it with chocolate chips.Refrigerate it for 2-3 hours and enjoy!