Beat the butter with the powdered sugar into a fluffy a cream, and while continuously beating add the egg yolks one by one, and then, 2-3 tablespoons flour. Separately, put the black coffee and the Nescafe with milk and granulated sugar to boil.
Remove from the heat and add the mixture with the egg yolks and flour while continuously beating. Return to the heat and stir until thickened. Separately, beat the egg whites into fluffy cream and finally mix gently with the now cooled cream with coffee.
Spread a bit of cream along the bottom and sides of an oven dish. Dip each biscotti in a mixture of milk and 1 teaspoon of Nescafe. Arrange a row of biscuits, cream and repeat, until out of ingredients.
Top with plenty of cream, sprinkle with 1 tablespoon Mocha coffee and 1 tablespoon cocoa.