Separate the egg whites from the yolks. Beat the whites with the sugar to fluffy snow. Add the yolks 1 by 1, stirring carefully. In a bowl, mix the flour, walnuts and baking powder.
Add them gradually to the eggs, while stirring with a spatula. Divide up the resulting mixture into 2-3 parts (I did 3). Bake each layer in a rectangular 9 3/4″ (25 cm) x 13 3/4″ (35 cm) form with baking paper. Be careful not to over-bake - 356°F (180 °C) for 8-10 min.
Make the vanilla cream according to packet directions. Boil 2 1/2 cups (600 ml) of the milk with the sugar. Dissolve the flour in the rest of the milk and add it to the boiling milk. Stir until thickened. Leave it to cool and add it to the prepared vanilla cream.
Beat the butter with the powdered sugar and add to the cream. Beat well to a smooth cream.
Place 1 layer in a suitable platter. Smear it with part of the cream. Cover with a 2nd layer, cream again, cake layer and finish off with cream.
Cut the bananas in 2 lengthwise. Arrange them on top of the cream, even off the ends.
Melt the chocolate in the heated cream with the butter. Pour this glaze over the bananas. For the decoration, beat the cream and smear the entire cake with it, putting extra on the top.
Put the cake in the fridge for several hours.
Take it out and decorate with cream rosettes, pieces of bananas and melted chocolate.