Oatmeal Rhubarb Bars with Buttery Crumble Topping

Name: Oatmeal Rhubarb Bars
Prep time: 10 min
Cook time: 35 min
Total time: 45 min
Cuisine: American
Ingredients: 5 to 6 stalks rhubarb (3 cups chopped); Chopped pecans; Old fashioned rolled oats; 1 cup unsalted butter, melted and cooled; Cinnamon; Ground ginger; Pinch of nutmeg (optional); All purpose flour; Brown sugar; Granulated sugar; Cornstarch; Salt; Baking soda; Large egg

By:

Ruby Bennett

Published:

June 7, 2026

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The Perfect Summer Dessert

There is something about rhubarb that sets my heart a pitter patter. When the first bright pink stalks appear at the farmers market, I know spring has truly arrived. And my favorite way to celebrate? These Oatmeal Rhubarb Bars.

Think of them as a portable fruit crisp with a buttery oat and pecan crust, a tangy sweet rhubarb filling, and a crumble topping that shatters with every bite. They work for everything: a casual weeknight dessert, a potluck contribution, or a lunchbox surprise. Serve them warm with vanilla ice cream or at room temperature for a picnic. Either way, they disappear fast.

Here’s what makes these Rhubarb Bars SO GOOD:

Buttery crisp texture. Old fashioned rolled oats and chopped pecans create a crust and topping that stays crunchy, not soggy. The secret is using melted butter and not overmixing the crumble.
Flavor packed in every layer. Ground ginger in the rhubarb filling adds warmth, while cinnamon in the oat mixture complements the natural tartness. A squeeze of lemon juice brightens everything.
Make ahead and freezer friendly. These bars keep for days at room temperature and freeze beautifully for up to three months. That means you can prep them for summer BBQs or holiday gatherings well in advance.

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Key Ingredients for Old Fashioned Rhubarb Bars

These bars prove that rhubarb does not need strawberry to shine. It is a strong fruit that can stand on its own two stalks. Here is what you need:

Rhubarb. About 5 to 6 stalks yield 3 cups chopped. Look for firm, crisp stalks. If using frozen rhubarb, thaw and drain the excess liquid so the filling does not get soggy.
Nuts and oats. Chopped pecans add crunch, and old fashioned rolled oats give the crust and topping a hearty texture. Quick oats will not work as well; they turn mushy.
Butter. One full cup of unsalted butter, melted and cooled, creates a rich, tender crumb. Do not use margarine.
Warm spices. Cinnamon goes into the crust; ground ginger goes into the filling. A pinch of nutmeg works too if you have it on hand.
Baking staples. All purpose flour, brown sugar, granulated sugar, cornstarch, salt, baking soda, and a large egg hold everything together.

How to Make Our Rhubarb Oatmeal Bars

This recipe comes together in four easy steps. The filling cooks while you mix the crust, so the total time is about 45 minutes.

Step 1: Make the rhubarb filling. In a medium saucepan, combine 3 cups chopped rhubarb, 1 cup granulated sugar, 2 tablespoons cornstarch, 1/4 cup water, and 1/2 teaspoon ground ginger. Bring to a boil over medium heat, stirring often. Reduce the heat and simmer for 7 to 10 minutes, until the rhubarb softens and the mixture thickens. Remove from the heat and stir in a squeeze of fresh lemon juice. Set aside to cool slightly.

Step 2: Prepare the crust and crumble. In a large bowl, whisk together 2 cups all purpose flour, 1 1/2 cups old fashioned rolled oats, 1 cup packed brown sugar, 1 cup chopped pecans, 1 teaspoon ground cinnamon, 3/4 teaspoon Kosher salt, and 3/4 teaspoon baking soda. Pour in 1 cup melted unsalted butter and 1 beaten large egg. Stir with a fork until the mixture is evenly moistened and crumbly. Do not overmix or it will become dense.

Step 3: Assemble the bars. Grease a 9×13 inch baking pan or line it with parchment paper for easy cleanup. Press half of the crumb mixture firmly into the bottom of the pan. Spread the cooled rhubarb filling evenly over the crust. Sprinkle the remaining crumb mixture on top, covering the filling completely.

Step 4: Bake. Bake at 350 degrees F for 30 to 35 minutes, until the topping is golden brown and the filling is bubbly around the edges. Let the bars cool completely in the pan before slicing. This step is important: if you cut them while warm, the filling will run. Cooling allows the bars to set properly.

Tips & FAQs

How do you make oatmeal rhubarb bars?

Start by making a buttery brown sugar crust and oat crumble topping. Press most of the mixture into a 9×13 pan, then layer with a cooked rhubarb filling made from fresh or frozen rhubarb, sugar, and cornstarch. Sprinkle the remaining crumble on top and bake until golden and bubbly.

Should rhubarb bars be refrigerated?

Yes, because the rhubarb filling is moist and perishable. Store them in an airtight container in the refrigerator for up to 5 days. Let them come to room temperature for about 15 minutes before serving for the best texture.

Can you use frozen rhubarb for rhubarb bars?

Yes, you can use frozen rhubarb without thawing it first. Toss the frozen rhubarb with sugar and cornstarch, then cook the filling as directed. You may need to add a minute or two of extra cooking time to thicken the filling properly.

How do you thicken rhubarb filling for bars?

Cornstarch is the best thickener for rhubarb filling. Use about 2 to 3 tablespoons of cornstarch per pound of rhubarb. Cook the rhubarb with sugar and cornstarch over medium heat until the mixture thickens and becomes glossy before adding it to the crust.

What goes well with rhubarb bars?

Rhubarb bars pair beautifully with a scoop of vanilla ice cream, a dollop of whipped cream, or a drizzle of simple powdered sugar glaze. A sprinkle of chopped pecans or walnuts in the crumble topping adds nice crunch and flavor.

How long do rhubarb bars last?

Stored in an airtight container in the refrigerator, rhubarb bars will stay fresh for up to 5 days. For longer storage, freeze them for up to 3 months. They are best enjoyed within the first 2 to 3 days for optimal texture.

Oatmeal Rhubarb Bars

This recipe makes 16 generous bars. Prep time is about 10 minutes, cook time 35 minutes, total 45 minutes.

The buttery oat and pecan crust cradles a tangy sweet rhubarb filling, all topped with a golden crumble. Perfect for summer potlucks, family gatherings, or a simple weekday treat.

Ingredients 1x2x3x

For the crust and crumbles:

2 cups all purpose flour (spooned and leveled)
1 1/2 cups old fashioned rolled oats
1 cup packed brown sugar
1 cup chopped pecans
1 teaspoon ground cinnamon
3/4 teaspoon Kosher salt
3/4 teaspoon baking soda
1 cup unsalted butter, melted and cooled
1 large egg, beaten

For the rhubarb filling:

3 cups chopped rhubarb (about 5 to 6 stalks)
1 cup granulated sugar
2 tablespoons cornstarch
1/4 cup water
1/2 teaspoon ground ginger
Squeeze of fresh lemon juice

Instructions

Preheat the oven to 350 degrees F. Grease a 9×13 inch baking pan or line it with parchment paper.
Make the filling: In a medium saucepan, combine rhubarb, granulated sugar, cornstarch, water, and ginger. Bring to a boil over medium heat, stirring frequently. Reduce the heat and simmer for 7 to 10 minutes until thickened and the rhubarb is soft. Remove from heat, stir in lemon juice, and set aside to cool.
Make the crust and crumble: In a large bowl, whisk together flour, oats, brown sugar, pecans, cinnamon, salt, and baking soda. Add melted butter and beaten egg, and stir with a fork until the mixture is crumbly and evenly moistened.
Assemble: Press half of the crumb mixture firmly into the prepared pan. Spread the cooled rhubarb filling evenly over the crust. Sprinkle the remaining crumb mixture on top.
Bake for 30 to 35 minutes, until the topping is golden brown and the filling is bubbly. Cool completely in the pan before slicing into 16 bars.

Notes

These bars keep at room temperature for 3 to 4 days, or in the refrigerator for 5 to 7 days. For longer storage, freeze for up to 3 months. To re crisp, bake at 350 degrees F for 15 minutes. For a gluten free version, use a 1 to 1 gluten free baking flour blend and certified gluten free oats. Adjust the sugar in the filling based on the tartness of your rhubarb; very tart rhubarb may need a little extra.

Nutrition

Per serving (1 bar): 340 calories, 44g carbohydrates, 4g protein, 17g fat (8g saturated), 42mg cholesterol, 129mg sodium, 2g fiber, 24g sugar.

If you love rhubarb as much as I do, be sure to try my Amish Oatmeal Rhubarb Bars With Crumb Topping and these Rhubarb Crumble Cheesecake Bars for more ways to enjoy this seasonal star. For another take on classic rhubarb bars, check out this rhubarb crumble bars recipe from King Arthur Baking.

Oatmeal Rhubarb Bars with Buttery Crumble Topping

The Perfect Summer Dessert

Here’s what makes these Rhubarb Bars SO GOOD:

Key Ingredients for Old Fashioned Rhubarb Bars

How to Make Our Rhubarb Oatmeal Bars