Cream the warmed butter, sugar and egg in a large bowl. Then add the flour mixed with baking powder, vanilla sugar, lemon zest and coffee.
Pour the batter into a greased or paper-lined baking pan (you can use a loaf pan, a cake pan or a baking tray).
Bake at approx. 175 °C (convection oven) for at least 45 minutes, then check and bake for another 10 minutes if necessary.
Preparation Tip:
If you like, you can cover the coffee cake with currant jam and chocolate or sugar icing or just dust it with powdered sugar. Without any coating it looks a bit boring, but in terms of taste it would not need any glaze.