Layer: Separate the egg whites from the yolks. Beat the egg whites with 1/2 cup sugar to stiff peaks. In another bowl, beat the yolks with 1/2 cup sugar until fluffy. Add 2/5 cup (100 ml) milk and the oil, then the baking powder, sifted flour and ground walnuts. Carefully stir with the egg white cream. Pour it into a round form with baking paper. Bake in a preheated 356°F (180 °C) oven about 45 min., depending on the oven.
For the creams: make each pudding separately, as follows.
Pour 2 cups (500 ml) milk and 1 cup sugar in a pot. Put on the stove, once boiling pour in the pudding dissolved in 2/5 cup (100 ml) water ahead of time. Repeat the procedure for the other 2 pudding creams.
Cut the cooled cake layer into 3.
Put the uppermost layer with the crust facing down in a cake platter and smear with 1/2 the banana cream. Arrange the sliced banana on top and smear with the remaining cream. Place the middle layer and smear 1/2 the chocolate cream, arrange coarse pieces of chocolate and smear with the remaining cream. Place the last layer with the bottom facing up and smear with 1/2 the vanilla cream. Smear the remaining cream along the sides. To make it easier use a form with removable walls.
Decorate with roasted halved walnuts and sprinkled crumbled roasted ones. After 6 hours in the fridge it'll be ready to eat.