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Freshly baked Raspberry Rhubarb Slab Pie with golden lattice crust, served on a sheet pan and cut into squares

Raspberry Rhubarb Slab Pie

This Raspberry Rhubarb Slab Pie is a sweet-tart summer dessert made with a buttery crust, juicy raspberries, and tangy rhubarb. It’s the perfect make-ahead treat for picnics, potlucks, or family dinners—easy to slice, share, and fall in love with.
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Equipment

  • Rimmed baking sheet (10x15 inch)
  • Rolling Pin
  • Mixing bowls
  • Whisk
  • Pastry brush
  • Knife or pizza cutter

Ingredients
  

  • 2 pie crusts store-bought or homemade
  • 2 ½ cups rhubarb chopped
  • 2 cups fresh raspberries
  • 1 ¼ cups granulated sugar
  • ¼ cup cornstarch
  • 1 tablespoon lemon juice
  • ½ teaspoon vanilla extract
  • 1 egg beaten (for egg wash)
  • Optional: coarse sugar for sprinkling

Instructions
 

  • Preheat oven to 400°F (200°C). Line or lightly grease a 10x15" sheet pan.
  • Roll out one pie crust and fit it into the bottom of the pan, leaving slight overhang on edges.
  • In a large bowl, gently mix rhubarb, raspberries, sugar, cornstarch, lemon juice, and vanilla.
  • Spread the fruit mixture evenly over the crust.
  • Roll out the second crust and cut into strips to form a lattice top (or lay it flat with steam vents).
  • Seal edges, brush top with egg wash, and sprinkle with coarse sugar if using.
  • Bake for 35–40 minutes, or until the crust is golden and the filling is bubbling.
  • Let cool completely before slicing.

Notes

You can substitute raspberries with strawberries, blackberries, or a berry mix.
If using frozen fruit, thaw and drain well before mixing.
The pie cuts best once fully cooled and filling is set.
Store at room temperature for 2 days, or refrigerate for up to 5 days.
Wrap slices tightly to freeze for up to 3 months.