Raspberry Rhubarb Slab Pie

One of the first fruits to appear at farmers markets every spring, bright pink rhubarb is such a cheerful fruit. Sweet-tart rhubarb is at its best in this raspberry rhubarb slab pie recipe. Ripe, juicy raspberries balance pucker-y rhubarb, and the berries’ hot pink color enhances rhubarb’s natural rosiness. Enormous sheets of pastry make this slab pie big enough to share with a crowd—or save leftovers for tomorrow’s breakfast.

If you’ve never tried slab pie before, it’s a fun twist on your favorite pie recipes. Slab pies are long and thin, meaning you get extra crust in every bite—think Pop-Tarts or fancy pastries. Because the filling is spread thinner, it’s easier to use moist ingredients, like fresh fruit, without ending up with soggy pastry. Finally, making homemade pie crust can be a bit fussy, so you might as well make an extra-large rhubarb and raspberry pie and get more bang for your buck.

Raspberry Rhubarb Slab Pie Ingredients

Pie Crust

• All-purpose flour: Make sure to measure flour properly, scooping flour into the cup with a spoon and then scraping the cup even with a knife. Using too much flour can make the crust tough.
• Salt: A pinch of salt draws out the flavors of both the pastry and the fruit.
• Butter: The secret to the best pie crust? Use very cold butter.
• Milk: Adding milk to the pastry adds rich flavor and makes the dough easy to roll out. We use 2%, but you can easily swap in whole or skim, if you prefer.
• Egg yolk: Enrich the dough with an egg yolk, which adds flavorful fat and protein that helps bind the crust together. After separating the egg, reserve the white for another use.

Filling

• Sugar: Use plain granulated sugar here. It will help thicken the fruit juice as well as sweeten up the piquant rhubarb.
• Cornstarch: Cornstarch is a powerful thickener that absorbs excess juice from the fruit so you can avoid soggy pie crust.
• Raspberries: Use fresh or frozen raspberries in this pie. If using frozen, measure them while frozen, then thaw and drain the berries before using.
• Rhubarb: In season, sliced fresh rhubarb is a refreshing, juicy treat. You can also use frozen rhubarb: Measure it when frozen, then thaw and drain the excess juice. No need to press on the fruit to extract all the juice.

Vanilla Icing

• Confectioners’ sugar: Also known as powdered sugar, confectioners’ sugar is light and easy to stir up with milk to create an easy icing.
• Vanilla extract: A dash of vanilla flavors the frosting.
• Milk: Add just enough milk to give the icing the proper consistency: not too thin or too thick. We call for 2%, but again feel free to use whole or skim.

Directions

Step 1: Start the pie dough

In a large bowl, whisk together the flour and salt. Using two knives, a pastry cutter or your fingers, cut in the butter in small chunks. Work it into the flour until the mixture looks crumbly.

Step 2: Add the liquid ingredients

Whisk the egg yolk into 3/4 cup milk. Gradually pour the egg yolk and milk into the flour mixture, tossing with a fork. Add additional milk, 1 tablespoon at a time, if necessary, until the dough is just moist enough to form a ball.

Editor’s Tip: Don’t add extra milk just because it seems as if it will make the dough easier to roll out. Extra milk can make the pastry tough. Stop as soon as the dough just holds together.

Step 3: Divide and chill

Divide the dough into two portions. Make one slightly bigger than the other (the base crust needs to be rolled larger than the top). Wrap each dough ball in storage wrap, and refrigerate the dough for about an hour or until it is firm enough to be easy to handle.

Editor’s Tip: Don’t skip the chilling! It makes the dough easier to work with and chills the butter again so the pastry will be nice and flaky.

Step 4: Roll out the bottom crust

Preheat the oven to 375°F. Take the larger dough portion out of the refrigerator. Roll out the dough between two sheets of lightly floured waxed paper into an 18×13-inch rectangle. Using the waxed paper to help lift, transfer the crust to an ungreased 15x10x1-inch baking pan. Press the crust onto the bottom and up the sides of pan. Trim any excess crust so it lines up with the edges of the pan.

Step 5: Make the filling

In a large bowl, stir together the sugar and cornstarch. Add the raspberries and rhubarb, tossing to coat. Spoon the filling into the crust.

Editor’s Tip: You’re aiming for the fruit to be evenly distributed across the pie, but it doesn’t have to be perfect.

Step 6: Roll out the top crust

Roll out the remaining dough on another piece of floured waxed paper. Carefully lift the crust and place it over the filling.

Step 7: Seal the pie

Fold the bottom crust over the edges of the top crust. Pinch to close, then press with a fork to seal and make a decorative edge. Prick all over the top of the crust with a fork.

Editor’s Tip: Pricking the top crust releases excess steam so the top is crispy. This will prevent a soggy pie crust.

Step 8: Bake the pie

Bake until the crust is golden brown, 45-55 minutes. Set on a wire rack to cool completely.

Step 9: Make the icing

While the pie cools, make the icing. Whisk together the confectioners’ sugar, vanilla and just enough milk to achieve a drizzling consistency.

Editor’s Tip: If the icing is too thick, add more milk, 1 teaspoon at a time. If it’s too runny, add more sugar, one spoonful at a time.

Step 10: Ice the pie

With a spoon, drizzle the icing over the pie. Cut the pie into squares to serve.

Raspberry Rhubarb Slab Pie Variations

• Change up the fruit: Rhubarb is also delicious with other berries, such as strawberries, blackberries or blueberries.
• Spice it up: Boost the flavor of the fruit filling with a pinch of spice. Cinnamon, cardamon or star anise are tasty pairings with rhubarb. Herbs such as rosemary or lavender are tasty too.
• Add a sweet topping: Skip the icing and top the rhubarb and raspberry pie with a crunchy sugar layer instead. Before baking, crack an egg into a small bowl and whisk well. Brush the egg over the top crust, then sprinkle crunchy sugar, such as turbinado, over the pie. You could also sprinkle the top with cinnamon sugar.

How to Store Raspberry Rhubarb Slab Pie

Store rhubarb raspberry pie in a cool, dry place, away from direct light. Wait for it to cool completely, then wrap it tightly in storage wrap or cover the pan with foil. If you don’t plan to eat the slab pie for a few days, store it in the refrigerator.

How long does raspberry rhubarb slab pie last?

On the counter, slab pie will keep for about two days. In the fridge, the pie keeps well for up to four days. The crust will soften a bit as it sits, but it will still taste good. To crisp it back up, reheat the pie in the toaster oven.

Can you freeze raspberry rhubarb pie?

Yes, pie freezes very well, including this slab pie! Make sure the pie is completely cool. You can freeze the entire pie, tightly wrapped in at least two layers, such as storage wrap and foil. Or, cut the pie into squares, wrap each square tightly and then freeze. Store the pie in the freezer for up to two months. Defrost it in the refrigerator overnight before serving.

Raspberry Rhubarb Slab Pie Tips

Can you use raspberry rhubarb filling in a regularly shaped pie?

Absolutely, you can make a classic pie with raspberry rhubarb filling. Following our strawberry rhubarb pie recipe, simply replace the strawberries with raspberries.

What can you serve with raspberry rhubarb slab pie?

Rhubarb and raspberry pie is one of our favorite summer desserts. Naturally, it tastes delicious at a picnic, following classics like pasta salad and sandwiches. Or, the fruity pie is delightful after an easy grilled dinner. Since the pie is big and keeps well at room temperature, it’s also a great choice for a potluck dessert.

One unexpected way to eat slab pie? For breakfast! The lightly sweet pastry makes a delightful dessert-style breakfast. Serve it with a dollop of yogurt.