1. Preheat the Oven:
Set your oven to 350°F (175°C). This gives it time to heat evenly while you prep.

2. Line the Pan:
Line a 9×13-inch baking dish with parchment paper, leaving an overhang on the sides for easy lifting later.

3. Make the Shortbread Crust:
In a large bowl, whisk together flour, sugar, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture looks like coarse crumbs.

4. Press and Bake:
Press the crust mixture evenly into the bottom of the prepared pan. Use a flat-bottomed glass or measuring cup to smooth it out.
Bake for 15–20 minutes until lightly golden around the edges.

5. Mix the Filling:
In a separate bowl, stir together the chopped rhubarb and sugar. Add cornstarch, vanilla, salt, and beaten eggs. Mix until no streaks remain and everything is well combined.

6. Rest the Mixture:
Let the filling sit for 10 minutes. This gives the rhubarb time to release its juices, ensuring a soft and flavorful bake.

7. Assemble:
Once the crust is partially baked, pour the rhubarb mixture evenly over the hot crust.

8. Bake Again:
Return the pan to the oven and bake for 30–35 minutes, or until the filling is set and just lightly golden on top.

9. Cool Completely:
Let the bars cool in the pan on a wire rack until fully set. Don’t rush this step—they slice best once chilled.

10. Slice and Serve:
Use the parchment paper overhang to lift the bars from the pan. Slice into squares and serve as-is or with a dusting of powdered sugar for a pretty finish.