Preheat your oven to 350°F (175°C) and grease or line a 13x9 inch baking dish with parchment paper.

In a medium mixing bowl, combine 2 cups of all-purpose flour and 1/4 cup of granulated sugar. Blend in 1 cup of softened unsalted butter until it resembles coarse crumbs, then press into the prepared dish.

Bake the crust in the preheated oven for 15 minutes or until lightly golden.

While the crust bakes, whisk together 3 eggs, 2 cups of granulated sugar, 1/3 cup of all-purpose flour, and 1/2 teaspoon of salt in a bowl until smooth.

Fold in 4 cups of diced rhubarb until well coated.

Pour the rhubarb mixture over the baked crust and spread evenly. Return to oven and bake for 40-45 minutes until filling is set and golden.

Allow to cool completely in the pan before cutting into squares and serving.