Preheat the oven to 200 ° C and lightly grease the casserole dish or small portion gratin dishes.
Wash and prepare the rhubarb, peel if necessary and cut into small pieces. Mix the mascarpone with the milk until smooth, this is best done with a hand blender.
Then add sugar, vanilla sugar, salt and beaten eggs. Distribute the rhubarb pieces in the mold or forms, pour the topping over them and cook in the oven for 40 minutes until the mixture has thickened and is slightly browned.
Smaller molds can be removed after 20 - 30 minutes.