Preheat your oven to 350°F (175°C). Gather your equipment.

In a mixing bowl, combine flour, cold butter, and confectioners' sugar. Mix until the mixture resembles coarse sand.

Press the mixture evenly into the bottom of the prepared baking dish.

Bake the crust for 15 minutes until lightly golden.

Chop rhubarb into 1/2-inch pieces and set aside while the crust bakes.

Whisk together brown sugar, white sugar, eggs, a bit of flour, salt, and vanilla until smooth.

Fold the chopped rhubarb into the custard mixture.

Pour the rhubarb custard filling over the crust and bake for about 40 minutes.

Cool for 10 minutes, then cut into bars and let cool completely for 30-45 minutes.