Grease the baking tray (approx. 35 x 40 cm). Clean, wash and drain the rhubarb. Cut into pieces of about 1 cm. Separate the eggs and put the egg white in a fat-free mixing bowl
Cream fat, 150 g sugar, vanillin sugar and salt with the whisk of the hand mixer. Stir in the egg yolks one by one. Mix flour and baking powder. Alternate with the milk and stir briefly in portions
Spread the fairly firm dough with a moistened dough card on the baking tray. Beat the egg whites and 1 pinch of salt until stiff, while continuing to beat, pour in 200 g of sugar. Keep beating until the sugar is dissolved
Fold almonds and rhubarb into the beaten egg white. Spread the rhubarb and meringue mixture evenly over the dough. Bake in the preheated oven (electric cooker: 200 °C/recirculating air: 175 °C/ gas: level 3) for 30-35 minutes. Take out and let cool down
Dust the rhubarb cake with icing sugar. Decorate with lemon balm if desired. Serve with lightly whipped cream and roasted almond flakes as desired
Instead of almonds you can also use hazelnuts for the meringue layer. As fruits you can also use currants or gooseberries