Rinse and clean the rhubarb. Cut off the top and cut them into smaller pieces.
Mix the soft butter with the sugar, vanilla sugar, baking powder and flour. Mix/knead until the mixture resembles coarse crumbs.
Distribute 2/3 of the crumble dough in a pie dish. We used a rectangular dish but a circular (20-23 cm / 8-9 inch) would work just fine. Use your fingers; press the dough into the shape of the pie dish.
Distribute the cut rhubarb on top of the dough.
Distribute the last crumble dough on top of the rhubarb. Sprinkle with chopped almonds.
Bake the pie at 175 C (350 F) for about 30-35 minutes.