Melt butter in a pot. Separate the eggs. Beat the egg whites, 3 tablespoons of water and 1 pinch of salt with the whisk of the hand mixer until stiff, adding sugar
Stir in the egg yolks one after the other. Mix flour, starch, tea powder and baking powder, sieve onto the egg mixture and fold in. Carefully fold in butter as well. Pour the sponge cake into a greased, flour-spread ring cake mould (approx. 1 litre capacity)
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 30 minutes, remove from oven. Leave the cake to cool in the tin for approx. 5 minutes, turn out onto a cake rack. Let it cool down for about 2 hours, dust with icing sugar
waiting time approx. 2 hours