Beat the butter, sugar and eggs until frothy. Fold in all the other ingredients, lastly the flour mixed with baking powder. Spread on a baking sheet that has been greased or lined with baking paper. Bake at 175 ° C (hot air 150 ° C) for about 35 minutes.
After cooling, cover with the icing and cut into approx. 3 cm squares.
Tip: For children, use lemon juice instead of rum for the topping.