Separate the egg whites from the yolks and put them in two different mixing bowls. Add the sugar to the yolks and blend. Now add the mascarpone and use the whisk to obtain a smooth mixture. Whisk the egg-whites until they are stiff and add them into to the mascarpone mixture. Spread a thin layer of the obtained mixture in a oven-proof dish. Dip the Osvego biscuits in cold coffee, to which you have added a little milk, then arrange a layer of the biscuits over the cream mixture. Proceed as described above in order to get 3 layers of cream and 2 layers of soaked Osvego biscuits.
Place in refrigerator. Before serving, sprinkle cocoa powder and chocolate chips on top of the tiramisu.