Cream butter with sugar, vanilla sugar, rum, lemon zest and salt. Gradually add yolks and egg, finally fold in flour. Fill the mixture into a piping bag with any kind of nozzle, pipe small sticks or other shapes and bake in the preheated oven at 165 to 175 °C for about 10 minutes until light brown. Spread half of the cooled tongues with jam or cream on the underside and place the other half on top. Dip up to half in chocolate icing.