Preheat your oven to 350°F (175°C). In a large mixing bowl, whisk together 1 ½ cups all-purpose flour and ½ cup powdered sugar until well combined. Cut in ¾ cup of cold, cubed butter using a pastry cutter or your fingertips, until the mixture resembles coarse crumbs. Firmly press this mixture into a greased 9x13-inch pan and bake for 15 minutes, until the edges turn golden and fragrant.

While the crust bakes, prepare the filling by mixing 2 cups of chopped rhubarb with 1 cup of granulated sugar in a medium bowl. Stir until the rhubarb releases its juices. In another bowl, lightly beat 2 eggs, then stir in ¼ cup of flour and ½ teaspoon of vanilla extract. Combine this egg mixture with the rhubarb.

Once the crust is ready, pour the rhubarb filling over it, spreading it evenly across the surface. Return the pan to the oven and bake for 30 to 35 minutes until the filling is set.

After baking, remove the pan from the oven and allow the bars to cool completely. Transfer the pan to the refrigerator and chill for at least one hour before slicing into squares.