Preheat the oven to 200C.
Cut off the leaves of the rhubarb. Wash the stalks and slice them into 5/6cm pieces.
Place 50 gr of sugar in a frying pan. Add 5cl of water and bring to a boil. Add the rhubarb sticks and cook over low heat for 10 minutes.
In the meantime, melt the butter in a small saucepan. In a mixing bowl, mix 100gr of sugar with the eggs until the mixture whitens. Add the flour, the vanilla seeds, the baking powder and the melted butter and mix thoroughly.
Butter a springform cake tin, nicely place the rhubarb sticks in the bottom of the tin. Sprinkle with the cooking juice and add the cake mixture.
Bake for 35 minutes.
Once cooked, allow to cool and then carefully turn out onto a serving plate. This cake is best served at room temperature, with vanilla ice cream, lightly whipped cream or custard.