Mix the butter and powdered sugar until creamy than loosely add the egg yolk and rum. On a silicone baking paper, bake a round sheet at 220 °C, for approximately 12 minutes using the metal ring found in the mould.

Beat the eggs with sugar and then add oil, potato flakes, baking powder and flour. After that add the water, the dried vegetables, chives and the citric acid. Grease the mould with Tarant spray. Fill this mixed dough into a mould. Bake it for 10 minutes at 160 °C. Take out the baked dough from the oven, put it on a tray and turn it upside down. Remove the silicon mould and the metal ring from the dough. Cut the sponge cake into smaller parts.