01 -
Preheat the oven to 180°C (350°F).
02 -
In a bowl, combine flour, powdered sugar, and cold butter. Mix until crumbly. Add the egg and vanilla extract, then knead until a smooth dough forms. Wrap in plastic wrap and refrigerate for 30 minutes.
03 -
In another bowl, mix the chopped rhubarb with granulated sugar and cornstarch. Set aside.
04 -
Roll out the chilled dough on a floured surface and place it into a tart pan. Trim the edges and pierce the bottom with a fork.
05 -
Bake the crust in the preheated oven for 15 minutes.
06 -
While the crust is baking, prepare the crumble topping by mixing flour, butter, brown sugar, oats, and cinnamon until crumbly.
07 -
Remove the crust from the oven, add the rhubarb filling, and sprinkle the crumble topping over it.
08 -
Bake for an additional 25 minutes or until the topping is golden brown.
09 -
Allow to cool before serving.