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An overhead photo of a berry slab pie in a cookie sheet with a lattice crust on top.
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Triple Berry Rhubarb Slab Pie

This yummy simple triple berry rhubarb slab pie - a pastry pie in bar form - is baked up with 3 berries and rhubarb for all the rhubarb lovers out there.
Prep Time45 minutes
Cook Time1 hour
Chilling Time2 hours
Total Time3 hours 45 minutes
Course: Dessert
Servings: 18
Calories: 301kcal
Author: Ellen

Equipment

Ingredients

For the Pie Crusts:

  • 3 3/4 cups all purpose flour
  • 1 1/2 cups unsalted butter (cold, and diced into small pieces)1
  • 1.5 tsp salt
  • 3/4 cup half and half (plus a little extra as needed)

For the Triple Berry Rhubarb Filling:

  • 3 cups diced rhubarb
  • 5 cups mixed berries
  • 1 cup sugar
  • 1/4 cup cornstarch
  • 1 TBS fresh lemon juice

For Topping:

  • 1 large egg
  • 1 TBS milk (or half and half)
  • 1/4 cup coarse sugar (optional)

For the Optional Icing:

  • 2 cups powdered sugar
  • 2 TBS milk
  • 1/2 tsp vanilla extract
  • 1/2 tsp almond extract

Instructions

Pastry Dough

  • Add the flour and salt to a large bowl.
  • Add in the diced butter and cut it into the flour with a pastry cutter, or two forks until its a nice even consistency with some pea sized pieces throughout.
  • Drizzle the cold half and half into the dough while mixing with a rubber spatula. Then dust your hands in flour and work the dough together until you can make a nice soft dough.
  • Divide the dough in half and wrap each half in plastic wrap. Place it in the fridge for at least 2 hours.
  • Preheat the oven to 375 degrees
  • Remove one of the pastry dough balls from the fridge and roll it out onto a piece of parchment paper. Roll it into a rectangle that is approximately 13x18inch, and about 1/4inch thick.
  • Carefully transfer the paper and pie crust to a 10x15 inch jelly roll pan. Leave the extra crust hanging over the sides for now.

Triple Berry Rhubarb Filling

  • Add the berries and rhubarb to a large bowl.
  • Add in the cornstarch, sugar, and lemon juice and toss them all together. Let it sit in the bowl for about 10 minutes, or until the berries begin to emit their juices.
  • Scoop the berry mixture evenly into the prepared pie crust in the jelly roll pan, using a slotted spoon to leave the extra juices behind in the bowl.
  • Roll out the second pie crust to the same size as the first. Cut it into 1 inch wide strips. Lay them diagonally across the baking pan. Alternate strips the other direction, laying them over and under the already laid strips to make a lattice crust.
  • Cut off any extra pie crust at the edges and pinch the top and bottom crusts together with your hands.

For Topping:

  • Add the egg to a small bowl and whisk it until combined.
  • Add in the milk and whisk it into the egg.
  • Brush the egg wash over the top of the pie crust with a rubber brush.
  • Sprinkle coarse sugar evenly over the top of the pie crust.
  • Bake the pie for 50 to 60 minutes, or until the crust is golden brown and the filling is nice and bubbly. **
  • Remove the pie from the oven and set the pan on a wire rack to cool for at least 30 minutes.

For the Optional Icing:

  • Add the powdered sugar to a bowl. Stir in 2 TBS of the milk, and the vanilla and almond extract until you can stir it smooth.
  • Add a little more powdered sugar as milk to make a nice drizzle-able consistency.
  • Drizzle over the top of the slightly cooled pie.
  • Serve the pie warm (it will be more messy/juicy) or let it cool completely for better even slices.

Notes

**I like to make sure the filling is bubbling for at least 5 to 10 minutes in the oven to make sure it will set after the pie has cooled down. 

Nutrition

Serving: 1g | Calories: 301kcal | Carbohydrates: 53g | Protein: 3g | Fat: 9g | Saturated Fat: 6g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 2g | Trans Fat: 1g | Cholesterol: 37mg | Sodium: 176mg | Potassium: 98mg | Fiber: 1g | Sugar: 37g | Vitamin A: 306IU | Vitamin C: 2mg | Calcium: 35mg | Iron: 1mg