Wash and peel the rhubarb and cut into pieces about 1/2 cm long. Mix with the raw cane sugar and let stand for about 1/2 hour.
In the meantime, prepare the crumble. To do this, melt the butter, let it cool, knead with flour, salt, vanilla sugar and powdered sugar in a food processor with the dough hook until the mixture crumbles. Place in the refrigerator.
For the dough, mix the room-warm butter with sugar and lemon zest. Gradually add the eggs. Mix the flour with the baking soda and fold in.
Spread the mixture on a baking tray lined with baking paper, spread the rhubarb pieces on top and sprinkle with the crumble.
Bake in the oven at 180 °C for about 30 minutes.