How to make
For the layer, beat the egg with the sugar, vanilla sugar and part of the milk into a cream. Add the remaining milk, walnuts, oil, while stirring after each one.
Mix the sifted flour with the baking powder, stir, add to the mixture and stir again. Pour the mixture into an oiled and floured rectangular oven dish and bake at 340°F (170 °C) for 25 min. Leave the baked layer to cool.
In the meantime, make the cream: add the starch, vanilla sugar and sugar to the cold milk, stir. Put it on low heat and boil until the cream thickens, while stirring nonstop.
Shortly before taking it off the stove, add the diced butter, stir until completely melted and until you obtain a smooth cream.
Pour the cream over the cake layer, distribute it evenly, sprinkle with coarsely ground walnuts. Leave the cake for at least 2 hours before serving.
