Preheat the oven to 350°F (175°C).

In a medium bowl, combine 1 cup all-purpose flour and 1/4 cup granulated sugar for the crust.

Cut in 1/2 cup softened unsalted butter until the mixture resembles coarse crumbs.

Press the crust mixture into the bottom of a 9x9 inch baking pan.

Bake the crust in the preheated oven for 15 minutes, or until the edges start to turn golden.

In a large bowl, whisk together 1 cup granulated sugar, 2 tablespoons all-purpose flour, 1/2 teaspoon baking powder, and 1/4 teaspoon salt for the filling.

Beat in 2 large eggs until the filling mixture is smooth and well combined.

Gently fold in 2 cups diced fresh rhubarb until evenly distributed.

Pour the rhubarb filling over the pre-baked crust, spreading it out evenly.

Return the pan to the oven and bake for an additional 40-45 minutes, or until the top is set and lightly golden.

Allow the bars to cool completely in the pan on a wire rack.

Once cooled, cut into squares.