Preheat the oven to 180 degrees. Lay out a baking dish with parchment paper.
For the crumble, melt the butter and allow to cool. With the K-Beater, stir the cooled butter with the flour, salt, vanilla and granulated sugar into a crumble. As soon as crumbs form, switch off the kitchen machine and place the crumbs in the fridge.
Wash the rhubarb, peel if necessary and cut into pieces of 0.5cm. Mix the rhubarb pieces with the granulated sugar. Mix with the flour just before use.
For the batter, beat the warm butter with the icing sugar for a few minutes until creamy. Add the eggs one at a time and stir. Mix the flour with the salt and baking powder, add to the mix, and mix well.
Spread the batter evenly in the baking dish lined with baking paper. Distribute the rhubarb pieces on top. Finally, distribute the chilled crumble over it.
Bake the rhubarb cake in a preheated oven for about 45-50 minutes.
Once cooked, remove from the oven and allow to cool.
Once cool, sprinkle with icing sugar, cut into pieces and serve.
Serve with a scoop of vanilla ice cream or freshly whipped cream, and garnish with fresh mint.