These rhubarb shortbread bars combine a buttery shortbread crust with a bright, tangy rhubarb filling for a simple spring dessert that feels nostalgic, fresh, and easy to bake.
Preheat the oven to 350°F and line a 9-inch square baking pan with parchment paper.
In a mixing bowl, combine flour, 1/4 cup sugar, and salt.
Add the cold cubed butter and rub it into the flour mixture until coarse crumbs form.
Press the crust mixture firmly into the prepared baking pan, reaching all corners evenly.
Bake the crust for 15 minutes until lightly golden around the edges.
While the crust bakes, stir together chopped rhubarb, remaining sugar, cornstarch, lemon juice, vanilla extract, and optional cinnamon in a bowl.
Spoon the rhubarb filling evenly over the hot crust.
Bake for 30 to 35 minutes until the rhubarb softens and bubbles around the edges.
Cool the bars completely at room temperature.
Refrigerate the bars for at least 1 hour before slicing into squares.
Slice and serve chilled or at room temperature.
Notes
For clean slices, chill the bars for at least 1 hour before cutting. Fresh rhubarb gives the best flavor and texture, but frozen rhubarb works if thawed and drained thoroughly. Dust with powdered sugar before serving if desired.