A rustic yet elegant dessert featuring a buttery shortbread crust, tangy rhubarb filling, and a crunchy oat crumble topping. Perfect for spring and summer, served warm with ice cream or chilled with coffee.
Preheat oven to 375°F (190°C). Grease a 9-inch tart pan with a removable bottom.
To make the crust, combine 1 1/4 cups flour and 1/4 cup sugar in a bowl. Cut in 1/2 cup cold butter until mixture resembles coarse crumbs. Add cold water 1 tablespoon at a time until dough just comes together.
Press dough evenly into bottom and sides of tart pan. Prick with a fork and bake for 10 minutes. Remove and let cool slightly.
In a bowl, mix chopped rhubarb, 1/2 cup sugar, cornstarch, and vanilla. Spread evenly over pre-baked crust.
For the crumble topping, mix 1/2 cup flour, oats, brown sugar, and cinnamon. Cut in 1/4 cup cold butter until crumbly. Sprinkle over rhubarb filling.
Bake for 35-40 minutes or until topping is golden and filling is bubbling.
Let cool before removing from tart pan. Serve warm or chilled, optionally with whipped cream or ice cream.