Stir 3 tablespoons of starch with a little milk into a paste. Add the resulting mix to the rest of the milk. Whip 2 egg yolks with 1-2 tablespoons granulated sugar until whitened and add to the milk mixture as well.
Put this on the heat and keep stirring, until thickened. Cool and add 1 packet of vanilla. Separately, beat the butter with the powdered sugar, add the cocoa while stirring, along with the second packet of vanilla, and finally - the walnuts. Slowly add the cooled milk cream to the mixture, spoon by spoon.
Add the egg whites, that you've beaten to snow with 5 tablespoons granulated sugar. Dip the biscotti in the milk, to which you have added rum or cognac - 1 tbsp, then arrange them in 1 row in a cake tray.
Top with a thick layer of the cream. Arrange the remaining biscotti, fill the gaps with pieces and smear with the remaining cream, form the sides of the cake and sprinkle it with ground walnuts.
You can decorate the cake with various fruits if you wish.