Raspberry Rhubarb Crumble Bars are bright, buttery dessert bars with a ruby-red fruit filling and a walnut crumble topping. The filling brings together rhubarb, raspberries, sugar, lemon juice, and cornstarch. The crust and topping are made from flour, quick oats, brown sugar, salt, baking powder, cinnamon, melted butter, and chopped walnuts.
These Raspberry-Rhubarb Crumble Bars make 12 bars. The prep time is 15 minutes, the cook time is 35 minutes, and the total time is 50 minutes. The recipe card describes them as tangy and sweet, with a walnut crumble topping and a raspberry rhubarb filling in one bite-sized package.
The method is straightforward but thoughtful. First, the pan is buttered and lined with parchment. Then the fruit filling is simmered until thickened and cooled. While that cools, the crumble crust is mixed. Most of the crumble mixture is pressed into the pan as the base, 1 cup is reserved for the topping, and the filling is spread between those two layers. Chopped walnuts finish the top before baking.
Rhubarb and Raspberries – A Perfect Match
Rhubarb and raspberries are a strong pair because both bring brightness, but they do it in different ways. Rhubarb has a firm, tart character that softens as it cooks. Raspberries bring juicy sweetness and a deep red color. Together, they make a filling that is tangy, sweet, and vivid.
The filling is cooked on the stovetop before the bars are assembled. This matters because the rhubarb needs time to start breaking down, and the cornstarch needs heat to thicken the juices. After about 10 minutes of simmering, the filling should be thickened, with the rhubarb starting to break down. Cooling the filling before spreading it over the crust helps the layers stay more distinct.
Lemon juice adds more brightness, while sugar balances the tart fruit. The finished filling sits between a buttery oat crust and a crumbly walnut topping, so every bar has fruit, crunch, and soft crumble in the same bite.
Ingredients
For the filling, you need 1 1/2 cups rhubarb cut into 1/2-inch pieces, 1 1/2 cups fresh or frozen raspberries, 1/2 cup sugar, 2 tablespoons lemon juice, and 1 1/2 tablespoons cornstarch.
For the crumble crust, you need 1 1/4 cup flour, 1/2 cup quick oats, 1/2 cup brown sugar, 1/2 teaspoon salt, 1/2 teaspoon baking powder, 1/2 teaspoon cinnamon, 1/2 cup melted butter, and 1/2 cup chopped walnuts.
This is a practical dessert bar ingredient list. The same crumble mixture becomes both the bottom crust and the topping, which keeps the process simple. The walnuts are scattered over the top, adding texture and a nutty finish.
How to Bake Raspberry Rhubarb Crumble Bars
Preheat the oven to 350°F. Lightly butter an 8×8-inch square pan and line it with parchment paper, leaving an overhang on either side. Lightly butter the parchment and set the pan aside. The parchment overhang helps later when it is time to lift the cooled bars out of the pan.
Make the filling first. In a small saucepan set over medium heat, bring the rhubarb, raspberries, sugar, lemon juice, and cornstarch to a simmer. Cook, stirring occasionally, for about 10 minutes, or until the filling is thickened and the rhubarb is starting to break down. Remove the pan from the heat and set the filling aside to cool.
While the filling cools, prepare the crumble crust. In a large mixing bowl, combine the flour, quick oats, brown sugar, salt, baking powder, and cinnamon. Drizzle in the melted butter and stir until the mixture forms loose crumbs.
Set aside 1 cup of the crumble mixture for the topping. Press the rest into the prepared baking pan. Use the bottom of a glass or measuring cup to form an even layer. Spread the cooled filling onto the crust. Crumble the reserved topping evenly over the filling, then scatter the chopped walnuts over the top.
Bake for 30 to 35 minutes, or until the filling is bubbly around the edges and the topping is lightly golden. Let the bars cool completely in the pan. Transfer them to a cutting board and cut into 12 bars.
Variations on This Recipe
The recipe allows fresh or frozen raspberries, so you can use either based on what you have. The rhubarb is cut into 1/2-inch pieces, which helps it cook into the filling in about 10 minutes. Keep that size in mind if you want the filling to thicken properly before assembling the bars.
The crumble topping includes walnuts, but the main structure comes from the flour, oats, brown sugar, baking powder, cinnamon, and butter. The walnuts add crunch on top rather than being mixed into the full crumble base. That placement gives the bars a clear crust, fruit center, and nutty top.
Because these are bars, the cooling step is important. Cutting too early can make the filling run and the crust crumble unevenly. Letting them cool completely in the pan gives the layers time to set.
Tips for Clean Slices
Line the pan with parchment and leave an overhang on either side. This makes it easier to lift the cooled bars out as one piece before cutting. Buttering the pan and the parchment also helps with release.
Press the crust firmly and evenly. The recipe suggests using the bottom of a glass or measuring cup, which helps make a flat base. A firm base supports the fruit filling and makes the bars easier to slice.
Cool the filling before spreading it onto the crust. A hot filling can soften the base too quickly before baking. The recipe specifically sets the filling aside to cool after it thickens.
Let the finished bars cool completely before cutting. The recipe gives this instruction for a reason: the filling needs time to settle and the crumble needs time to firm up. If you like small-format desserts, Oreo and Nutella stuffed cookies are another handheld treat.
Storage Note
The recipe card states that the bars will keep for up to 3 days in an airtight container. Because they are already cut into 12 bars, they are easy to store once fully cooled. For more guidance on frozen fruit, freezing fruits can help when you are using berries or rhubarb from the freezer.
Frequently Asked Questions
Can I use frozen raspberries?
Yes. The recipe calls for fresh or frozen raspberries.
How many bars does the recipe make?
This recipe makes 12 bars.
Why cook the filling before baking?
The filling is simmered so it thickens and the rhubarb starts to break down before it is spread over the crust.
How do I know the bars are done?
Bake until the filling is bubbly around the edges and the topping is lightly golden. The bake time is 30 to 35 minutes.
A Bright Bar Dessert with a Buttery Crumble
Raspberry-Rhubarb Crumble Bars are easy to love because they bring several textures into one small dessert: a pressed oat crust, thick fruit filling, loose crumble, and chopped walnuts. The raspberries and rhubarb give the bars their sweet-tart flavor, while the cinnamon and brown sugar make the crumble warm and cozy. With 12 bars in one 8×8-inch pan, this is a useful dessert for sharing or keeping on hand for a few days. For another berry-friendly dessert idea, berry Greek yogurt parfait with granola keeps fruit at the center.
Raspberry-Rhubarb Crumble Bars
Equipment
- 8×8-inch square pan
- Parchment Paper
- Small saucepan
- Large mixing bowl
Ingredients
Filling
- 1 ½ cups rhubarb cut into ½” pieces
- 1 ½ cups fresh or frozen raspberries
- ½ cup sugar
- 2 tbsp lemon juice
- 1 ½ tbsp cornstarch
Crumble Crust
- 1 ¼ cup flour
- ½ cup quick oats
- ½ cup brown sugar
- ½ tsp salt
- ½ tsp baking powder
- ½ tsp cinnamon
- ½ cup butter melted
- ½ cup chopped walnuts
Instructions
- Preheat oven to 350F. Lightly butter an 8×8″ square pan and line with a piece of parchment paper, leaving an overhang on either side. Lightly butter the parchment. Set aside.
- Prepare the filling. In a small saucepan set over medium heat, bring the filling ingredients to a simmer. Cook, stirring occasionally, for about 10 minutes or until the filling is thickened and rhubarb is starting to break down. Remove from heat and set aside to cool.
- Meanwhile, prepare the crumble crust. In a large mixing bowl, combine flour, oats, sugar, salt, baking powder and cinnamon. Drizzle in the melted butter, and stir until the mixture forms loose crumbs.
- Set aside 1 cup of the mixture for the topping. Press the remainder into the prepared baking pan, using the bottom of a glass or measuring cup to form an even layer. Spread the cooled filling onto the crust. Crumble the reserved topping evenly onto the filling, then scatter chopped walnuts over top.
- Bake in preheated oven for 30-35 minutes, or until the filling is bubbly around the edges and topping is lightly golden. Let cool completely in the pan, then transfer to a cutting board and cut into 12 bars. Bars will keep for up to 3 days in an airtight container.
Notes
- Stay Crumble and Kind: Raspberry Rhubarb Crumble Bars Are a Sweet-Tart Treat - April 24, 2026
- Skillet Peach Rhubarb Crisp Is a Cozy Fruit Dessert - April 24, 2026
- Rhubarb Frangipane Tart Is a Beautiful Sweet-Tart Bake - April 24, 2026
