📖 Instructions

1. **Prepare the Crust:** Preheat your oven to 350°F (175°C). In a large bowl, whisk together 1 1/2 cups all-purpose flour, 1/2 cup (1 stick) cold unsalted butter cut into small cubes, 1/4 cup powdered sugar, and a pinch of salt. Use a pastry blender or your fingertips to cut the butter into the flour until the mixture resembles coarse crumbs. Pro Tip: Keep the butter as cold as possible for a flakier crust!
2. **Press the Crust:** Add 3-4 tablespoons of ice water, one tablespoon at a time, mixing until the dough just comes together. Do not overmix! Press the dough evenly into the bottom of an ungreased 9x13 inch baking pan. Prick the crust all over with a fork to prevent it from puffing up during baking.
3. **Bake the Crust:** Bake the crust for 15-20 minutes, or until it's lightly golden brown. Let it cool slightly while you prepare the rhubarb filling.
4. **Make the Rhubarb Filling:** While the crust is baking, in a medium saucepan, combine 4 cups of chopped rhubarb, 3/4 cup granulated sugar, and 2 tablespoons of cornstarch. Add 1/4 cup of water and stir well to combine.
5. **Cook the Rhubarb Filling:** Cook the rhubarb mixture over medium heat, stirring constantly, until it comes to a boil and thickens. This should take about 5-7 minutes. Remove from heat and set aside to cool slightly. Taste and adjust sweetness if needed. I like mine a bit tart, but you might prefer it sweeter! Careful as this can burn.
6. **Prepare the Custard Topping:** In a large bowl, whisk together 4 large egg yolks, 1/2 cup granulated sugar, 2 tablespoons all-purpose flour, and 1/4 teaspoon salt until smooth.
7. **Temper the Eggs:** In a separate saucepan, heat 2 cups of milk until it's just simmering. Slowly drizzle the hot milk into the egg yolk mixture, whisking constantly to prevent the eggs from scrambling. This is a crucial step, so take your time!
8. **Cook the Custard:** Pour the custard mixture back into the saucepan and cook over medium heat, stirring constantly, until the custard thickens and coats the back of a spoon. This should take about 5-7 minutes. Remove from heat and stir in 1 teaspoon of vanilla extract.
9. **Assemble the Squares:** Pour the cooled rhubarb filling over the pre-baked crust, spreading it evenly. Then, gently pour the custard topping over the rhubarb filling.
10. **Bake the Squares:** Bake the squares in the preheated oven for another 25-30 minutes, or until the custard is set and lightly golden brown. The center should be mostly firm with a slight jiggle. Watch out though. Keep an eye on it.
11. **Cool and Serve:** Let the squares cool completely in the pan before cutting them into squares. Dust with powdered sugar before serving, if desired. These are best served chilled, so I like to pop them in the fridge for a couple of hours before digging in! Honestly, I usually can't wait that long. You know?