Preheat your oven to 350°F (175°C) to prepare for baking these delicious lemon rhubarb bars. While the oven warms up, gather your ingredients, including flour, sugar, and cold butter, so you're ready to whip up the crust quickly.

In a large mixing bowl, combine flour, sugar, and salt. Use a whisk to blend them thoroughly until evenly mixed.

Add cold, cubed butter into the dry mixture. Using a pastry cutter or your fingertips, rub the butter into the flour mixture until it resembles coarse breadcrumbs.

Press the crumbly mixture firmly into the bottom of a greased 9x13 inch baking dish. Bake this crust in the preheated oven for 20 minutes or until it turns lightly golden.

While the crust bakes, prepare the filling by blending together 1 cup of sliced rhubarb, eggs, and freshly squeezed lemon juice in a blender or food processor until smooth.

In a separate mixing bowl, stir together the remaining sugar and flour. Add the blended rhubarb mixture, along with lemon zest and vanilla extract, and mix until well combined.

Gently fold the remaining rhubarb slices into your filling mixture.

Pour the filling over the pre-baked crust, spreading it out evenly. Return the baking dish to the oven and bake for an additional 35 minutes.

Once baked, remove the dish from the oven and allow it to cool completely at room temperature. Then transfer the dish to the refrigerator for at least 2 hours.