Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease the mould with butter and dust with flour.
For the sponge mixture, sieve 350 g flour into a bowl and mix with baking powder. Add 200 g butter, sugar, eggs, milk and orange peel. Using the whisks of the mixer, mix to a smooth dough, first on a small and then on the highest setting.
Fill into the mould, smooth it down. Bake the cake on the lower shelf in a hot oven for 50-60 minutes. Approx. 10 minutes before the end of the baking time, check with a long wooden stick whether the cake is ready.
If there is still soft dough sticking to the skewer, bake for another 5-10 minutes.
For the syrup squeeze oranges and lemon. Heat the juices in a pot and dissolve the icing sugar in them. Prick the finished cake several times and sprinkle with syrup. Let it cool down.
Falling onto a cake rack. Soak the whole cake with syrup again. Let it cool down.