Beat the butter and sugar until frothy, then gradually stir in the eggs. Mix the flour, lemon zest, pudding powder and baking powder and stir in as well. Line a baking sheet with parchment paper or grease it and spread the batter over it. Bake at top / bottom heat at 180-190 ° C for 20-25 minutes.
Make a frosting from the lemon juice and powdered sugar and spread on the cooled cake.