For the rabarber cake, mix all dough ingredients with the dough hook to a shortcrust dough and let it rest covered in the refrigerator for at least one hour.
In the meantime, wash and peel the rhubarb and cut into small pieces. Preheat the oven to 180 degrees.
Grease a baking tray (28 cm diameter) or line with baking paper. Roll out the dough and place it in the baking pan.
Press a border of about three centimeters. Prick the bottom several times with a fork. Spread the rhubarb on top and bake for 20 minutes.
For the topping, mix the remaining ingredients together and spread evenly over the rhubarb.
Turn the oven down to 175 degrees and bake the cake for another 25 to 30 minutes until light brown.
Remove the rhubarb cake from the pan and let it cool on a rack.