Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish.
In a medium bowl, combine 1 cup of flour, 1/4 cup of sugar, and 1/2 teaspoon of salt for the crust. Add the cold cubed butter and mix until crumbly.
Press the mixture evenly into the bottom of the prepared baking dish. Bake for 15 minutes until lightly golden.
While the crust is baking, prepare the filling. In a large bowl, combine the diced rhubarb, 1 cup of sugar, 1/4 cup of flour, and salt.
In another bowl, whisk together the eggs, milk, and vanilla extract. Gradually add the egg mixture to the rhubarb mixture, stirring until well combined.
Pour the rhubarb filling over the pre-baked crust. Bake for an additional 30-35 minutes, or until the filling is set and the top is lightly browned.
Allow to cool completely in the pan before cutting into bars.
Serve chilled or at room temperature.