For the sponge mixture, beat the fat and sugar with the whisk of the hand mixer until foamy. Stir in egg and egg yolk one after the other. Add salt, vanilla sugar, lemon peel and milk.
Mix flour and baking powder, then gradually stir in. Spread the dough into two springforms (24 cm Ø) greased at the bottom and sprinkled with breadcrumbs. For the meringue, beat the egg whites until stiff, allowing the sugar to trickle in.
Beat until the sugar is completely dissolved. Spread the meringue onto the surface of the sponge mixture. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for approx. 25 minutes. Remove and let cool off.
For the filling, soak gelatine in plenty of cold water. Clean, wash and cut the rhubarb into small pieces. Heat the redcurrant jelly. Sauté the rhubarb in it. Let it cool down a little. Squeeze the gelatine well, then dissolve in it.
Cool until the mass begins to stiffen. Whip the cream until stiff, pour in the vanilla sugar. Carefully fold into the rhubarb mixture. Cover one half of the base with a cake ring. Spread the filling on top.
Place the second meringue as a lid on top. Refrigerate again. Sprinkle with pistachios before serving. Makes about 16 pieces.