Beat soft butter, sugar, and vanilla sugar until creamy. This step is important and shouldn’t be skipped. Add lemon zest and part of the lemon juice, and mix. Add eggs individually and mix well after each egg. The batter should now be creamy and beige or light yellow. It’s best to use free-range eggs, as they are better for the hens and give a nicer color to the cake.
Mix cornstarch, flour, and baking powder in a second bowl. Sift flour and baking powder first. Instead of flour, you can use ground almonds or hazelnuts (the gluten-free alternative). Add dry ingredients to butter mixture and mix well. Add yogurt with a cooking spoon. The batter should be light and fluffy, but not runny, similar to the consistency of Nutella.
Grease cake pan (I used a small 18-cm round one) and pour batter into pan. Bake approx. 50 min. at 170°C/350°F. As temperatures can vary from oven to oven, use wooden skewer to test cake for doneness. If skewer comes out dry, cake is done.
Prepare icing while cake is baking. Sift confectioner’s sugar and mix well with part of the lemon juice. Best to use a teaspoon or small whisk. Pour icing over cake when it’s still warm and decorate as you fancy. I used lime zest. Enjoy!