Preheat the oven to 180°C.
Grease a gratin dish with butter, sprinkle with wheat flour and set aside.
In the bowl of a food processor with a blade attachment, mix the eggs, flour, milk, ALSACE LAIT low-fat crème fraîche for whipping, caster sugar and vanilla sugar. Mix for about 20 seconds.
Pour the mixture into the dish and add the rhubarb pieces. Bake in the oven for 55 minutes at 180°C.
Leave to cool.
It's now ready to enjoy!