These rhubarb bars are the perfect mix of sweet, tart, and buttery. They’re simple to make since the base and crumb topping come from the same oat mixture, with a thick layer of rhubarb jam baked in between. They can be made traditionally or gluten-free.
If you’ve never baked with rhubarb before, this is a great place to start! This Strawberry Rhubarb Crumble is also a great option.
As these bars cook, the rhubarb’s sharpness mellows into a soft, jammy filling that pairs perfectly with the oat layers.
This recipe is based on my Raspberry Oat Bars, but uses Rhubarb Preserves and fresh or frozen rhubarb in place of the raspberries. The bars look a bit different in the photos (because I used different photographers), but when I’ve made them myself, they turned out much more like the raspberry version – just with a less vibrant filling.
No matter how they look, you’ll get the same result! Soft, crumbly layers with a sweet-tart filling that slices beautifully once chilled.
If you do want a more vibrant filling, use my Strawberry Rhubarb Preserves in place of the homemade jam in today’s recipe. You’ll only need 1 cup, and since that recipe yields 1 2/3 cups, so you’ll have some leftover to enjoy on its own.
Ingredients
Scroll down for the full recipe. These are just a few notes on select ingredients.
- Rhubarb – fresh or frozen both work. If using frozen, there’s no need to thaw before cooking.
- Rolled oats – use old-fashioned oats, not quick oats. I tested these with quick oats, and they were delicious but way too crumbly.
- Butter – this should be soft enough to easily work into the flour mixture.
How to Make Them
First, cook the rhubarb, sugar, and lemon juice until thickened. It may not reach the typical jam-setting temperature, but it will continue to thicken as it cools and chills.
Let the jam cool completely before using.
For the crust and topping, mix the dry ingredients, then work in the butter until crumbly.
Press about two-thirds of the mixture into the pan, spread the jam over the top, and sprinkle with the remaining crumble.
Bake until golden and bubbling, then let the bars cool completely before chilling. This step is important for clean slices.
- Cook the jam long enough – even if it doesn’t hit 220 °F (104 °C), it should visibly thicken and pass the wrinkle test.
- Let the jam cool completely – adding warm jam can make the crust soggy and harder to layer.
- Press the crust firmly – this helps it hold together and prevents crumbly bars.
- Leave a border around the jam – this keeps it from bubbling over the edges while baking.
- Don’t skip chilling – these bars need time in the fridge to fully set. Cutting them too early will result in messy slices.
Troubleshooting
- Bars are too crumbly – the crust may not have been pressed firmly enough or the bars weren’t chilled long enough.
- Jam is too runny – it likely needed to cook longer. It should visibly thicken before cooling.
- Bars are too soft to cut – they need more chilling time. Refrigerate until fully firm.
- Bottom crust is soggy – the jam may have been too warm when added or too thin.
- Topping browned too quickly – your oven may run hot. Tent loosely with foil if needed.
How to Store and Freeze
Store the bars in an airtight container in the refrigerator for up to 5 days.
They freeze well, too. Place cut bars in an airtight container and freeze for up to 3 months. Thaw in the refrigerator overnight or at room temperature for about 30 minutes.
more Dessert Bar recipes
If these rhubarb bars aren’t for you, here are some other options.
- Berry Bars – super easy crumble bars filled with berries and jam, with options for gluten-free and vegan. I prefer the oatmeal mixture in today’s recipe because it’s a little less oily, but people are still loving those berry bars!
- Chocolate Raspberry Oat Bars – a richer twist with chocolate paired with tart raspberries in a sturdy oat base (the same one as the berry bars).
- Vegan Flapjacks – chewy oat bars sweetened with syrup, more like a snack bar but with that same cozy oat texture.
- No-Bake Paleo Lemon Bars – a completely different style, but still bright and tangy with a soft, no-bake base.
These rhubarb bars have a buttery oat crumble crust, a sweet-tart homemade rhubarb jam filling, and a golden crumb topping. Perfect for spring and early summer. Can be made traditionally or gluten-free.
Prevent your screen from going dark
Jam (or use 1 cup store-bought)
Prepare the jam
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Place a small plate in the freezer before you start cooking.
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To a 3-quart or larger saucepan (the larger the surface area, the less time you’ll need to cook them!), add the rhubarb, sugar and lemon juice.
3 cups (375 grams) fresh or frozen chopped rhubarb, 3/4 cup (150 grams) granulated sugar, 1 1/2 tablespoons lemon juice
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Bring to a boil over medium-high heat while stirring frequently. Turn the heat as low as possible while maintaining a full boil. Let boil for about 9 minutes, turning the heat down, if needed, towards the end to prevent the rhubarb from burning, until it reaches a temperature of 220 °F (104 °C). This is the temperature jam is said to set, but I couldn’t actually get mine above 212 °F (100 °C). It’ll still be a bit runny but will thicken as it cools and more as it’s chilled.
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When you think the jam is ready, drop a small spoonful onto the cold plate and let it sit for a minute. Push it with your finger – if it wrinkles and holds its shape, the jam is done.
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When it’s done, stir in the vanilla extract.
1 teaspoon vanilla extract
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Remove the saucepan to a wire rack to cool completely, about 1 hour.
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If not using right away, transfer to a clean jar and refrigerate for up to 1 week. Many sources say 2-3 weeks, but I like to play it safe and freeze whatever I haven’t eaten after 1 week. It also freezes great and can be frozen for up to 1 year. If using this jam immediately after making to make the bars, just make sure it’s room temp first. The bars also work if you use cold jam straight from the fridge.
Prepare the bars
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Preheat the oven to 350 °F (175 °C). Line an 8″x8″ pan with a piece of parchment paper.
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In a large mixing bowl, mix together the flour, oats, granulated sugar, brown sugar, baking soda, salt and cinnamon until everything is evenly combined.
2 cups (250-276 grams) flour, 2 cups (180 grams) rolled oats, 1/2 cup (100) granulated sugar, 1/2 cup (100) brown sugar, 1/2 teaspoon baking soda, 1/2 teaspoon salt, 1/2 teaspoon cinnamon
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Cut the butter into small cubes and add it to the dry mixture. Using your fingers, work the butter into the mixture until fully incorporated and the dough becomes crumbly but holds together easily when squeezed.
1 cup (225 grams) unsalted butter
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Once it starts forming clumps, drizzle the vanilla extract over the dough. Use your hands or a spoon to gently mix it in evenly.
1 teaspoon vanilla extract
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Scoop about 2/3 of the dough (roughly 582 grams or 2 2/3 cups) into the prepared pan. Press it firmly and evenly into the bottom to form the crust.
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Spread 1 cup of the rhubarb jam over the crust, leaving a small border of about 1/3″ around the edges (this will prevent the jam from leaking out the sides).
1 cup (275 grams) of the above jam
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Sprinkle the remaining crumble mixture evenly over the top of the jam. Lightly press the topping into the jam without flattening it too much. This is just to ensure that no pointy oat bits sticking up burn.
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Bake for 28-35 minutes or until the top is golden brown and slightly puffed, and the jam is bubbling around the edges. Remove to a cooling rack and let the bars cool completely in the pan, about 2 hours. Then chill for at least 2-3 hours or overnight before cutting.
- For the flour, you can use 2 cups (250 grams) all-purpose flour or for gluten-free, use 2 cups (250 grams) King Arthur Flour Gluten-free Measure for Measure Flour or 2 cups (276) grams Bob’s Red Mill 1-to-1 Gluten-free Baking Flour. Both worked great, but I think Bob’s was a little more sandy.
- The nutrition information provided is calculated as a courtesy and is only an estimate. I am not a licensed nutritionist or dietitian. For the most accurate nutritional data, consult a professional or use your preferred calculator.
Calories: 282.2kcalCarbohydrates: 40.3gProtein: 3.3gFat: 12.4gSaturated Fat: 7.4gPolyunsaturated Fat: 0.8gMonounsaturated Fat: 3.2gTrans Fat: 0.5gCholesterol: 30.5mgSodium: 112.2mgPotassium: 122.7mgFiber: 1.8gSugar: 20.8gVitamin A: 373.9IUVitamin C: 1.9mgCalcium: 33.8mgIron: 1.3mgNet Carbs: 39
