Preheat your oven to 350°F (175°C) and lightly grease a 9x13 inch baking pan.

In a medium bowl, combine 2 cups flour and powdered sugar. Cut in the cold butter using a pastry blender or two knives until the mixture resembles coarse crumbs.

Press the crust mixture firmly into the bottom of the prepared baking pan. Bake for 15 minutes or until the edges are very lightly browned.

While the crust is baking, prepare the filling by whisking the eggs in a large bowl. Add the granulated sugar, 1/2 cup flour, and salt, whisking until smooth.

Gently fold the chopped rhubarb into the egg mixture until evenly coated.

Pour the rhubarb mixture over the hot, pre-baked crust. Return to the oven and bake for an additional 40 to 45 minutes, or until the filling is set and the top is golden.

Remove from the oven and let the bars cool completely in the pan on a wire rack. For the cleanest slices, refrigerate for at least 2 hours before cutting into squares.