Rhubarb Oatmeal Bars

Name: Rhubarb Oatmeal Bars
Prep time: 15 min
Cook time: 35 min
Total time: 50 min
Ingredients: For the Crust and Crumb Topping; 1 1/2 cups old-fashioned rolled oats; 1 1/4 cups all-purpose flour; 3/4 cup brown sugar, packed; 1/2 teaspoon baking soda; 1/4 teaspoon salt; 3/4 cup unsalted butter, melted; For the Rhubarb Filling; 2 cups chopped fresh rhubarb; 1/2 cup granulated sugar; 1 tablespoon lemon juice; 1 tablespoon cornstarch; 1/4 cup water; 1/2 teaspoon vanilla extract

Author: Tracy Marger

Published: June 12, 2025

Updated: May 30, 2026

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Oatmeal Rhubarb Bars with Crumb Topping are a cozy, old-fashioned dessert with a buttery oat crust, a tangy rhubarb filling, and a golden crumb topping. They are soft, chewy, and just the right amount of sweet, making them a perfect treat for spring and summer baking. If you love rhubarb desserts with a rustic homemade feel, these bars are a great recipe to keep on hand.

Why You Will Love These Bars

These bars bring together everything people love about a good fruit bar: a sturdy base, a juicy filling, and a crumbly topping that bakes into a golden finish. The oats give the crust extra texture and a hearty flavor that pairs beautifully with the tart rhubarb. The filling cooks down into a bright, jammy layer with lemon juice and vanilla adding just enough depth to keep it balanced. They are simple to make, easy to slice, and perfect for sharing at gatherings, picnics, or afternoon coffee.

Ingredients

For the Crust and Crumb Topping

1 1/2 cups old-fashioned rolled oats
1 1/4 cups all-purpose flour
3/4 cup brown sugar, packed
1/2 teaspoon baking soda
1/4 teaspoon salt
3/4 cup unsalted butter, melted

For the Rhubarb Filling

2 cups chopped fresh rhubarb
1/2 cup granulated sugar
1 tablespoon lemon juice
1 tablespoon cornstarch
1/4 cup water
1/2 teaspoon vanilla extract

How to Make Oatmeal Rhubarb Bars with Crumb Topping

Step 1: Preheat and prepare the pan

Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper or lightly grease it. Lining the pan makes it easier to lift out the bars once they have cooled, and it also helps the crust bake more evenly.

Step 2: Make the oat crumb mixture

In a large mixing bowl, combine the oats, flour, brown sugar, baking soda, and salt. Pour in the melted butter and stir until the mixture becomes crumbly and evenly moistened. Reserve 1 cup of the mixture for the topping, then press the remaining mixture firmly into the bottom of the prepared pan to form the crust.

Step 3: Prepare the rhubarb filling

Add the chopped rhubarb, granulated sugar, lemon juice, and water to a saucepan over medium heat. Cook for 5 to 7 minutes until the rhubarb begins to soften. Stir in the cornstarch and continue cooking for another 1 to 2 minutes until the mixture thickens. Remove from the heat and stir in the vanilla extract. The filling should look glossy and slightly jammy.

Step 4: Assemble the bars

Spread the rhubarb filling evenly over the oat crust. Sprinkle the reserved oat mixture evenly over the top to create a crumb layer. Try to cover the filling without pressing the topping down too much so it stays light and crumbly after baking.

Step 5: Bake

Bake the bars for 30 to 35 minutes, or until the topping is golden and the filling is bubbling. The bubbling is a good sign that the rhubarb mixture has thickened properly. Remove the pan from the oven and let the bars cool completely before slicing.

Step 6: Slice and serve

Once fully cooled, cut the bars into squares. They can be served warm or chilled, depending on your preference. Warm bars have a softer texture, while chilled bars hold their shape more cleanly and taste especially refreshing.

Tips for Best Results

Use old-fashioned oats for the best texture since they create a more rustic and hearty crumb. If your rhubarb pieces are very thick, chop them a little smaller so they soften evenly in the filling. Do not skip the cornstarch because it helps the filling set properly and prevents the bars from becoming too loose. Let the bars cool fully before cutting, or the filling may spill out. For extra flavor, you can serve them with a scoop of vanilla ice cream or a little whipped cream.

Storage

Store Oatmeal Rhubarb Bars in an airtight container in the refrigerator for up to 5 days. They can be enjoyed cold or brought to room temperature before serving. If you want to freeze them, wrap individual bars tightly and store them for up to 2 months. Thaw in the refrigerator before eating.

FAQ

Can I use frozen rhubarb?

Yes, frozen rhubarb works well. Thaw it first and drain any excess liquid before using.

Can I make these bars ahead of time?

Yes, they are a great make-ahead dessert. In fact, they often slice even better after chilling.

Do these bars need to be refrigerated?

Yes, because of the fruit filling, they should be stored in the refrigerator after cooling.

Can I use quick oats instead of old-fashioned oats?

Old-fashioned oats are best because they give the bars better texture, but quick oats can work in a pinch.

What do these bars taste like?

They taste sweet, tart, buttery, and lightly chewy with a jammy rhubarb center and crisp oat topping.

Final Thoughts

Oatmeal Rhubarb Bars with Crumb Topping are a simple but satisfying dessert that highlights rhubarb in the best way. The buttery oat crust, soft fruit filling, and crumbly topping create a balance of textures and flavors that feels comforting and homemade. Whether you bake them for family, friends, or just to enjoy with a cup of tea, they are a reliable rhubarb treat worth repeating.