Mix butter, 100 g sugar, half of the lemon peel and 1 pinch of salt with the whisk of the hand mixer for 2-3 minutes until creamy. Stir in the eggs one after the other. Mix flour and baking powder. Alternately stir in flour, milk and 2 tbsp. lemon juice
Put the dough into a greased springform pan (26 cm Ø) sprinkled with flour and smooth it down. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes, remove from oven. Let the base in the tin cool down on a cake rack for about 2 hours
Wash the currants, pluck the berries from the panicles. Wash, clean and quarter the strawberries. Wash and clean the blueberries. Put aside about 50 g of each fruit. Wash lemon balm, shake dry. Pluck off leaves and chop finely
Soak gelatine in cold water. Mix buttermilk, 2-3 tbsp. lemon juice, remaining lemon peel and 50 g sugar. Squeeze the gelatine, dissolve it and stir in 2-3 tbsp. buttermilk. Stir into the remaining buttermilk. Chill buttermilk for about 5 minutes until it starts to gel.
Whip cream until stiff and fold in. Fold in fruit and lemon balm. Remove the base from the tin and surround with a cake ring. Pour the cream on top and spread it out smoothly, spread the remaining fruit on the cream. Chill for about 2 hours.
waiting time approx. 3 3/4 hours