Separate the egg whites from the yolks. Beat the yolks with the sugar until doubled in volume. Beat the whites to fluffy snow. Add the oil, flour and 1/4 of the beaten to snow egg whites to the egg yolk mixture. Beat a little while longer until homogeneous and add the rest of the yolks.
Prepare the mixture for the dark layer the same way, while also adding cocoa or powdered coffee to the flour. Bake the 2 cake layers at 392°F (200 °C) until ready. Let them cool while you make the cream.
Melt the butter in the milk that's boiling with the sugar. Dissolve the flour in plenty of water for a thick runny mixture and add it in a thin trickle to the boiling milk with the butter until you get a nice, smooth cream. Next, add the beaten yolk. Sprinkle with 1-2 vanilla packets and the cream is ready.
Begin assembling the cake. Cut out a ring from the white and dark layers, then another of each - for a total of 4 rings from the 2 layers and a small circle about 1 1/4″ (3 cm) in diameter in the middle of the layers.
Pour a thin layer of cream in a cake form, then place the largest ring of the white layer, going inward. Pour on cream to cover the walls and place the second largest ring from the dark layer, cream again and then the smaller light ring... etc, and finish off with the small light circle.
Pour cream on top and start arranging the second layer, beginning with the remaining rings - dark, light and so on. Decorate with cream on top and decorate as desired.