For the orange-walnut cake, preheat the oven to 180 °C. In a food processor, process the peeled and seeded oranges, sugar, vanilla sugar and butter until a thick batter is formed.
Add the whole eggs. Mix again. Add sifted flour and baking powder to the dough in stages in the food processor. Pour the dough into a greased baking pan and decorate the top of the cake mixture with walnuts.
Bake the cake for 30 to 35 minutes at 180 °C top/bottom heat. Remove the cake from the orange-walnut cake and let it cool.