These Buttery Rhubarb Shortbread Bars feature a rich, tender shortbread crust layered with a vibrant, tangy rhubarb filling and finished with a golden, buttery crumble topping. The contrast of sweet and tart flavors wrapped in a melt-in-your-mouth texture makes this dessert a seasonal favorite.
1 cup unsalted butter, softened
1/2 cup powdered sugar
2 cups all-purpose flour
1/4 teaspoon salt
1 cup rhubarb, chopped
1/2 cup granulated sugar
1 tablespoon cornstarch
1 teaspoon vanilla extract
1 tablespoon lemon juice
1 egg, lightly beaten (for brushing the top)