For the Barbara cake, beat the eggs and the room-warm butter until fluffy.
Stir in the icing sugar, vanilla sugar and the zest of 1 lemon until the sugar has dissolved.
Mix the two types of flour and the baking powder and fold in. Spread the dough in a greased loaf pan and bake in a preheated oven at 180° for about 1 hour (test with a stick).
For the glaze, squeeze the lemon and mix with 10dag of powdered sugar until you have a smooth glaze.
Spread it on the still warm barbara cake and let it set.