Mix the margarine with the sugar and vanilla sugar until frothy. Stir in the eggs one at a time for 1 minute each. Stir in the grated lemon zest, 1 tablespoon lemon juice and the yogurt. Mix the flour and baking powder and sift. Then stir in the flour twice.
Put the dough in a loaf pan that has been greased and dusted with flour and bake in the preheated oven (175 ° C top / bottom heat) on the middle rack for approx. 55 minutes (chopsticks test).
Let the cake cool for 10 minutes and take it out of the mold.
Make a glaze from 1 tablespoon lemon juice and powdered sugar, add a little more water if necessary, and brush the lukewarm cake with it.