Knead flour, baking powder, 50 g sugar and butter in flakes to a smooth dough. Cover and chill for about 30 minutes. Grease tart tin (24 cm Ø) and dust with flour. Roll out the dough on a floured work surface and place it in the form. Cut the edges of the dough smooth. Prick the base several times with a fork.
Cover with baking parchment, spread legumes on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 10 minutes until completely dark. Take out, remove baking paper with the pulses. Clean, wash and cut the rhubarb into pieces of approx. 2 cm width. Put juice, 50 g sugar, vanillin sugar and rhubarb in a pot, bring to the boil, cover and simmer for about 2 minutes. Stir pudding powder with 5-6 tablespoons of water until smooth. Remove the pot from the heat, stir in the custard powder and simmer for about 1 minute while stirring. Leave to cool down a little. Put the compote into the mould and smooth it down. Bake in the oven at the same temperature on the lower shelf for about 20 minutes. Beat the egg white until stiff, add 100 g sugar and salt.
Stir pudding powder with 5-6 tablespoons of water until smooth. Remove the pot from the heat, stir in the custard powder and simmer for about 1 minute while stirring. Leave to cool down a little. Put the compote into the mould and smooth it down. Bake in the oven at the same temperature on the lower shelf for about 20 minutes. Beat the egg white until stiff, add 100 g sugar and salt. Pour meringue mixture into a piping bag with a star-shaped spout. Spray it snake-shaped on the edge of the tart. Bake for another 5-8 minutes at the same temperature on the middle shelf. Let it cool down. Dust the rim with icing sugar
Pour meringue mixture into a piping bag with a star-shaped spout. Spray it snake-shaped on the edge of the tart. Bake for another 5-8 minutes at the same temperature on the middle shelf. Let it cool down. Dust the rim with icing sugar