📖 Instructions

1. Preheat the oven to 350°F (175°C). Lightly grease a 9x13 inch baking pan. Seriously, don't skip the greasing part or your bars will stick and you'll be sad.
2. In a large bowl, whisk together the flour, powdered sugar, and salt. This ensures everything is evenly distributed. Nobody wants a pocket of salt in their dessert!
3. Cut in the cold butter using a pastry blender or your fingers (if you're feeling ambitious!). The mixture should resemble coarse crumbs. Little chunks of butter are okay – they'll melt and create pockets of flakiness.
4. Press the crumb mixture evenly into the prepared baking pan. Use the bottom of a measuring cup to really pack it down. A compact base is key to a sturdy bar.
5. Bake for 15-20 minutes, or until the crust is lightly golden brown. Keep an eye on it! Ovens vary, and you don't want it to burn. Slightly underbaked is better than overbaked at this stage.
6. While the crust is baking, prepare the filling. In a large bowl, whisk together the eggs, granulated sugar, flour, melted butter, and vanilla extract. Make sure there aren't any lumps of flour.
7. Gently fold in the diced rhubarb and chopped pistachios. Don't overmix! Just enough to combine everything.
8. Pour the rhubarb mixture over the pre-baked crust, spreading it evenly. If the crust puffed up a little during baking, gently press it down before adding the filling.
9. Bake for 30-35 minutes, or until the filling is set and lightly golden brown. The center should be mostly firm – a slight jiggle is okay.
10. Let the bars cool completely in the pan before cutting into squares. This is important! If you try to cut them while they're still warm, they'll be a gooey mess.
11. Dust with powdered sugar, if desired. This adds a nice touch, but it's totally optional. Serve and enjoy! These bars are best enjoyed within a few days, but I doubt they'll last that long.