Preheat your oven to 375°F (190°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out later.

In a large bowl, whisk together the 2 cups all-purpose flour, 0.5 cup granulated sugar, and 0.25 tsp salt. Add the cubed cold butter and, using your fingers or a pastry blender, cut the butter into the dry ingredients until the mixture resembles coarse crumbs. Press the mixture evenly into the bottom of the prepared pan. Bake for 15 minutes, or until lightly golden. While the crust bakes, move on to the filling and topping.

In a medium bowl, using an electric mixer, beat the softened cream cheese until smooth. Add 0.5 cup granulated sugar and beat until well combined and fluffy. Beat in the large egg and vanilla extract until just incorporated. Don't overmix!

In a small saucepan, combine the chopped rhubarb, 0.25 cup granulated sugar, cornstarch, and water. Cook over medium heat, stirring occasionally, until the rhubarb has softened and the mixture has thickened, about 5-7 minutes. Set aside to cool slightly.

Pour the cream cheese filling over the warm, pre-baked crust and spread evenly. Spoon the rhubarb topping over the cream cheese layer. Return the pan to the oven and bake for 30-35 minutes, or until the edges are set and the center is only slightly jiggly.

Let the bars cool completely in the pan on a wire rack. For best results and clean cuts, refrigerate for at least 2 hours before lifting out of the pan using the parchment paper overhang and cutting into squares.