Preheat the oven to 160 degrees circulating air. Mix together 220 g butter, 170 g sugar, salt, lemon zest from 1 lemon and 1 tablespoon vanilla essence. Mix in the eggs one by one. Stir until the sugar has dissolved. Mix the spelled flour, potato starch and baking powder well. Stir alternately with the milk into the egg mixture. Pour the dough into a 25-30cm loaf tin lined with baking foil and bake until golden brown for 50-55 minutes. Make a chopstick test.
For soaking, boil 50 g butter, 50 g raw cane sugar, 1 tablespoon vanilla essence, lemon juice and zest from one lemon in a small saucepan until the sugar has dissolved.
Take the cake out of the oven and pierce it several times with a wooden stick while it is still hot, soak it well with the lemon icing and let it cool completely.