Bake a tart, yet buttery, dessert bar this summer. Made with chewy oats, these rhubarb crumble bars are easy to make from scratch. They’re a delicious treat to bring to barbecues and picnics!

rhubarb crumble bar showing layers of crumb and filling leaning on another bar.


 

Rhubarb doesn’t get enough attention in my opinion. When cooked with a bit of sugar, the bitter taste fades and a deliciously tart flavor emerges. It makes the perfect filling for crumb bars. The buttery oatmeal mixture envelops the rhubarb filling to create a treat for the tastebuds! Next, try baking an apple rhubarb pie.

Why You’ll Love This Recipe

  • Lovely seasonal flavor. Cooked rhubarb has a fresh tart flavor that is fitting for spring and early summer.
  • Perfect for picnics. Make a batch of dessert bars and bring them to your next picnic, barbecue or pool party!
  • Easy to make from scratch. The crumble mixture serves as the crust and topping. The filling comes together quickly on the stovetop.
  • Reliable recipe. I use the same recipe for the crust and crumble in many dessert bars, include my blueberry crumb bars and strawberry oatmeal bars.

Ingredient Notes

bowls of ingredients to make rhubarb crumble bars.
  • Oats: Rolled oats, also known as old-fashioned oats, are best for crumbles. Quick oats can work in a pinch, but I do not recommend steel cut oats since they are too tough.
  • Butter: Use unsalted butter that is softened, but still cool to the touch. Cut it into 1/2-inch pieces for easy mixing.
  • Rhubarb: Fresh rhubarb is best for baking. Be sure to remove the leaves and stems before dicing.
  • Cornstarch: To help thicken the filling, sprinkle some cornstarch into the filling mixture. Flour is a good substitution.
  • Lemon juice: A squeeze of fresh lemon juice helps brighten the natural rhubarb flavor. Fresh is preferred over bottled.

Refer to the recipe card for the full list of ingredients and measurements.

Recipe Variations

Add some strawberries. Dice up some strawberries and add it to the filling mixture. I suggest 1 cup strawberries and 1 cup rhubarb.

Top with a glaze. Whisk together 1/2 cup confectioners’ sugar with 1 Tablespoon fresh lemon juice for a simple lemon glaze. For a vanilla glaze, use 1/2 cup confectioners’ sugar with 1 teaspoon vanilla and 2 teaspoons milk or cream.

Double the recipe. Double all the ingredients and bake in a 9×13 baking pan for a larger batch. Baking time will be about the same, maybe a few minutes longer.

How to Make Rhubarb Crumble Bars

photo collage demonstrating how to make rhubarb crumble bars in a mixing bowl, 8x8 pan and medium saucepan.
  1. Make the crumble mixture. Whisk together flour, oats, brown sugar, sugar, baking powder and salt. Add the butter pieces and vanilla. Mix until the mixture small crumbles form.
  2. Transfer half the mixture to an 8×8 baking pan. Press down firmly to make the crust. Bake at 350 F for 20 minutes. Cool slightly.
  3. For the filling, cook rhubarb, sugar, cornstarch and lemon juice in a saucepan over medium heat until thickened. Cool slightly.
  4. Spread filling over crust. Sprinkle remaining crumble mixture over the top. Bake at 350 F for 30 to 35 minutes. Cool completely.

Expert Tips

Use fresh ingredients. Use rhubarb when it’s in season, May through July typically. It’s also important to use fresh lemon juice to help brighten the flavors.

Cook filling until thickened. If the mixture is too water it will make the bars soggy. It should coat the back of a spoon and be thick like fruit preserves.

Cool completely before serving. This is an important step to ensure the bars set up properly and aren’t messy.

rhubarb crumb bars cut into square on a tabletop next to a couple pieces of fresh rhubarb.

Make Ahead and Storage Tips

Make ahead the rhubarb mixture and store covered in the refrigerator for up to 48 hours. Bring to room temperature before using. You can also make ahead the crumble mixture. Cover the bowl with a damp kitchen cloth to prevent the mixture from drying out. Keep in the refrigerator for up to 48 hours.

Store rhubarb bars in an airtight container at room temperature for up to 3 days or in the refrigerator for 5 days.

Freeze bars for up to 3 months. Wrap bars in plastic wrap and place in an airtight container or freezer bag. Store in the freezer, then defrost in the refrigerator before bringing to room temperature.

Recipe FAQ

Can I use frozen rhubarb?

Yes, but it won’t have as much flavor. Defrost the rhubarb and discard the juices before making the filling.

Can I use this recipe to make a crisp?

There will be far to much crumble topping and not enough filling to make this into a crisp. I suggest using my strawberry rhubarb crisp recipe instead!

a couple rhubarb oatmeal bars on their side showing layers next to more bars on a tabletop.

Did you love this recipe? Please leave a 5-star 🌟🌟🌟🌟🌟 rating in the recipe card below and if you REALLY loved it, consider leaving a comment further down the page.

rhubarb crumble bar showing layers of crumb and filling leaning on another bar.

Get the Recipe: Rhubarb Crumble Bars

Bake a tart, yet buttery, dessert bar this summer. Made with chewy oats, these rhubarb crumble bars are easy to make from scratch.
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Ingredients

Crust and Topping

  • 1 ½ cups (187 g) all purpose flour
  • 1 ½ cups (150 g) rolled oats
  • cup (66 g) packed light brown sugar
  • cup (66 g) granulated sugar
  • ¼ teaspoon baking powder
  • ¼ teaspoon salt
  • ¾ cup (12 Tablespoons or 170 g) unsalted butter, softened, but still cool, cut into 1/2-inch pieces
  • 1 teaspoon vanilla extract

Rhubarb Filling

  • 2 cups (300 g) diced rhubarb
  • cup (100 g) granulated sugar
  • 1 Tablespoon cornstarch, or flour
  • 1 Tablespoon fresh lemon juice
  • Pinch of salt

Instructions 

  • Preheat oven to 350℉. Line a 8×8 baking dish with parchment paper and set aside.
  • In the bowl of a stand mixer (or using a hand mixer), combine flour, oats, brown sugar, granulated sugar, baking powder and salt. Mix for 30 seconds until thoroughly combined. With the mixer on low, add the butter and vanilla extract. Mix until the mixture resembles coarse sand (about 2 minutes).
  • Transfer half the mixture to prepared pan. Use your hands or the back of a measuring cup to press mixture evenly into the bottom to form the crust. Bake crust for 20 minutes or until golden (keep the oven on).
  • While the crust bakes, make the rhubarb filling. In a saucepan over medium heat, bring rhubarb, sugar, cornstarch, and lemon juice to a boil. Stir constantly until mixture is thickened, about 2 minutes. Remove from heat. Cool slightly.
  • Spread rhubarb mixture over baked crust. Sprinkle remaining oat mixture evenly over the fruit layer.
  • Bake bars for 30 to 35 minutes or until the rhubarb bubbles and the top is golden brown. Allow bars to cool completely before removing from pan and cutting into 16 squares.

Notes

Store covered in an airtight container at room temperature for up to 5 days or in the refrigerator for a week.
Freeze for up to 3 months. Wrap in plastic wrap and place in an airtight container in the freezer. Defrost in the refrigerator before bringing to room temperature.
Serving: 1bar, Calories: 203kcal, Carbohydrates: 28g, Protein: 2g, Fat: 9g, Saturated Fat: 6g, Polyunsaturated Fat: 1g, Monounsaturated Fat: 2g, Trans Fat: 0.3g, Cholesterol: 23mg, Sodium: 40mg, Potassium: 101mg, Fiber: 1g, Sugar: 13g, Vitamin A: 282IU, Vitamin C: 2mg, Calcium: 28mg, Iron: 1mg

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