Preheat the oven to 175 C.
Whisk the eggs, granulated sugar, syrup and vanilla sugar until white and really fluffy.
Melt the butter, add the milk with the saffron, and bring to the boil.
Combine the flour, baking powder and salt, and carefully fold in the egg mixture together with the saffron-flavoured milk.
Grease and sugar a cake tin. Fill it with the batter.
Bake the cake in the middle of the oven for 30-35 minutes. Use a wooden skewer to check: it should not come out without crumbs sticking to it.
Leave the cake to cool and then turn it upside down.
Dust the cake with icing sugar before serving.