Ingredients
For the crust:
- 3 ½ cups all-purpose flour
- 1 tablespoon sugar
- 1 teaspoon salt
- 1 ½ cups (3 sticks) cold unsalted butter, cubed
- 1 large egg
- ½ cup ice water (more if needed)
For the filling:
- 4 cups fresh rhubarb, chopped
- 3 cups fresh raspberries
- 1 ¼ cups granulated sugar (adjust to taste)
- ¼ cup cornstarch
- 1 tablespoon lemon juice
- 1 teaspoon vanilla extract
- 1 tablespoon butter, cut into small pieces
For assembly:
- 1 egg (beaten, for egg wash)
- 1 tablespoon coarse sugar (optional)
Instructions
- Make the crust:
In a large bowl, whisk together flour, sugar, and salt. Cut in the cold butter with a pastry cutter or your fingers until the mixture resembles coarse crumbs. In a small bowl, beat the egg with ice water. Gradually add to the flour mixture, mixing until the dough holds together. Divide in half, shape into disks, wrap in plastic wrap, and chill for at least 1 hour. - Preheat the oven:
Preheat your oven to 400°F (200°C). Line a large rimmed baking sheet with parchment paper. - Prepare the filling:
In a large bowl, gently toss rhubarb and raspberries with sugar, cornstarch, lemon juice, and vanilla extract. Let stand 10 minutes. - Assemble the pie:
On a floured surface, roll out one disk of dough into a large rectangle (about 12×17 inches) to fit your sheet pan. Transfer to the prepared pan, pressing into corners. Pour in the filling and dot with butter. - Top the pie:
Roll out the second disk of dough and place over the filling. Trim excess, fold edges under, and crimp. Cut a few slits on top to vent steam. Brush with egg wash and sprinkle with coarse sugar if desired. - Bake:
Bake for 40–50 minutes, or until the crust is golden and the filling is bubbling. If the crust is browning too quickly, tent loosely with foil. - Cool & serve:
Let the slab pie cool completely before slicing into squares. Serve as-is or with a scoop of vanilla ice cream!
If you’d like, I can help you create a quick glaze or a crumble topping too — just say so!