Rhubarb: In a bowl, toss the rhubarb pieces with the seeds from ½ vanilla bean and 100 g raw sugar. Let it sit for ½ hour.

Crumble: Scrape out the seeds from the other half of the vanilla bean and mix with the remaining 75 g raw sugar, butter, flour, and rolled oats. Crumble everything together well.

Grease an ovenproof dish with butter and add the rhubarb.

Spread the crumble over your rhubarb and bake the cake in a preheated oven at 180 degrees Celsius (356 degrees Fahrenheit) fan-forced for about 40 minutes, until the crumble is golden brown.

Serve the rhubarb crumble warm or cold with crème fraîche or vanilla ice cream.