This berry rhubarb slab pie is a delicious, juicy rhubarb and berry pie baked up in a sheet pan. It’s got a flaky buttery crust, juicy berry filling, and is perfect for a crowd.
I am so excited to share this Berry Rhubarb Slab Pie with you. I’m excited to share it with you, because it’s deliciously sweet from blueberries, raspberries, and blackberries – and just a little tangy from the rhubarb.
This rhubarb slab pie is a pie baked in a jelly roll pan instead of a a pie pan. This means it’s easy to make, perfect for a crowd, and can be served up like a cookie bar, or eaten with a fork. You might also love this Rhubarb Dump Cake.
This rhubarb and triple berry slab pie is delicious served warm, or after it’s cooled down. You will get neater slices if you’ve let the pie cool down completely before slicing and serving. Just warm the slice up in the microwave for a few seconds if you want to enjoy it warm again, and don’t forget a scoop of vanilla ice cream or whipped cream on top!
Ingredients Needed:
This is a quick overview of the ingredients you’ll need for this Berry Rhubarb Slab Pie recipe. Specific measurements and full recipe instructions are in the printable recipe card below.
- All Purpose Flour – the structure and main ingredient needed for a pie crust.
- Unsalted Butter – to cut into the flour, an all butter crust makes the pie crust extra flaky.
- Salt – to give the pie crust just a little flavor.
- Half and Half – using half and half instead of ice cold water makes this crust a little softer, and richer. You can substitute ice water if desired.
- Mixed Berries – you can use fresh berries or frozen berries for this recipe. If you’re using frozen let them thaw for about 30 minutes before using.
- Rhubarb – this adds a little tartness to the pie filling, and balances well with the berries sweetness.
- cornstarch – this helps thicken the berry mixture
- Granulated Sugar – this helps sweeten the berry mixture
- Lemon Juice – just a little bit to balance the sweetness of the fruit and help bring out the fruit’s natural flavors
- Egg – to brush the top of the crust with, to help it get extra golden when baking.
- Coarse Sugar – just a little for sprinkling on the crust before baking, this gives the pie crust an extra nice crunch.
How to make Berry Rhubarb Slab Pie?
While this recipe seems long and complicated, it’s not, it’s like making any ol’ pie, but with an even better crust to filling ratio, and it’s the perfect large dessert for a crowd!
Slab Pie Crust
Add the flour and salt to a large bowl. Add in the diced pieces of butter. Cut the butter into the flour with a pastry cutter, or two forks until it’s nice sand like consistency, with some pea sized pieces throughout.
Drizzle in the cold half and half and work it into the dough, use floured hands to work it together into a nice soft dough.
Divide the dough in half and flatten each ball into a 1inch rectangle. Wrap them up with plastic wrap and place them in the fridge for at least 2 hours.
Remove 1 of the pastry dough balls and roll it out to be a 13x18inch rectangle, about 1/4 inch thick. Transfer the pie crust carefully to a 10x15inch jelly roll pan lined with parchment paper cut for the bottom.
Berry and Rhubarb Filling
Add the berries and the rhubarb together to a large bowl.
Add in cornstarch, sugar and lemon juice and toss them all together. Let the mixture sit for about 10 minutes.
Scoop the berry mixture into the prepared pie crust in the pan. Use a slotted spoon to leave some of the berry juices behind in the bowl, and discard those. Spread the berry mixture evenly across the pie crust.
Finishing the Slab Pie
Roll out the remaining dough ball of pie crust dough, the same size as the first. You can top the pie with the whole crust, or make a lattice top with strips. Cut the dough into 1 inch wide strips, diagonally across the pie crust. Lay the strips diagonally across the berry filling, leaving a 1 inch space between each strip, then lay the strips the alternate direction, lifting the already laid strips as you go to make a lattice crust.
Whisk an egg in a small bowl, then add in the milk for the egg wash. Whisk them together. Using a silicone brush, brush the egg wash evenly over the top pie crust pieces.
Sprinkle the coarse sugar evenly over the top of the crust if desired. This adds a nice sparkle to the pie, and a delicious crunch as well.
Bake the slab pie until the crust is nicely golden brown and the filling has been bubbling for a few minutes.
Tips and Tricks:
- Berries are naturally juicy, and will excrete a lot of juices after you mix the ingredients together for the filling. Don’t pour the filling into the pie crust, but make sure to scoop it out of the bowl into the crust using a slotted spoon. This will leave the extra liquid behind, and help prevent a soggy bottom crust.
- Use your choice of mixed berries. For this pie I used blackberries, raspberries, and blueberries – but other good berries would be strawberries (chopped up small), huckleberries, boysenberries, etc.
- If you can’t find rhubarb, or it’s not rhubarb season you can still make this pie – just add another 3 cups of berries to substitute for the 3 cups of rhubarb.
- Add a Tablespoon or so of lemon zest to the berry mixture for a fun zesty, and fresh flavor.
- You can have the top crust of the pie be a whole crust (make sure to cut in some slits to let the filling steam escape, it can be fun to cut out shapes with a cookie cutter for different occasions) or a lattice crust as pictured.
- You can add a sweet icing to the top of the pie if desired. Mix together 2 TBS of milk (or half and half), 2 cups powdered sugar, and 1/2 tsp of each vanilla and almond extract. Drizzle it evenly over the slightly cooled pie.
How to store?
Store any leftover slab pie in an airtight container, or wrapped up in plastic wrap in the refrigerator for up to 4 days.
This berry rhubarb slab pie is one of the best summer desserts. It’s delicious on it’s own, or served with a scoop of ice cream on top. It’s perfect for a crowd, which makes it a great option for a potluck or barbecue!
Let the slab pie continue to cool before serving for ultimate thickening. If served warmed, which is delicious, the slab pie might be a little runny. Serve as is, with a scoop of ice cream, or whipped cream. Store any remaining triple berry rhubarb slab pie covered in the fridge.
This triple berry rhubarb slab pie is a beautiful and delicious dessert! It can be a bit time consuming but the results are well worth it, and you’ll want to eat it all spring and summer long!
More berry desserts:
If you make this key lime pie ice cream recipe, please let me know! Leave a 
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Triple Berry Rhubarb Slab Pie
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
Equipment
- 11×8 baking sheet
- Large Mixing Bowl
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 10×15 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
Nutrition
This triple berry rhubarb slab pie was first posted on June 12, 2014. The photos and text were updated for clarity on June 29, 2022.
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