Rhubarb Bars

At a glance

What stands out: Rhubarb bars are the reliable treat when rhubarb’s in season. Tart rhubarb is balanced by sweet strawberry preserves, then baked until jammy. With an irresistible crumble on top, rhubarb bars can be enjoyed with coffee or tea, or topped with a scoop of ice cream for a tasty dessert.

How long it takes: 15 minutes to prep, 1 hour in the oven, 1 hour to cool
Equipment you’ll need: 9 x 13 inch baking pan or dish
Servings: 24 bars

Are you a rhubarb lover or hater? We're firmly on the “love” side of the equation and these rhubarb bars are one of our favorite ways to use it.

Our mom grows the rhubarb in her backyard and so did our grandma and great-grandma. In fact, we believe our mom’s rhubarb plants are grown from cuttings received from our great-grandma. The thing about rhubarb is that its season is fleeting; it’s one of the first plants that can be harvested in the spring but once the weather gets warm, the stalks are too woody to eat.

So when rhubarb is ripe for the picking, you need to make ALL the rhubarb recipes: strawberry rhubarb crisp, rhubarb Instant Pot cake, and straightforward rhubarb sauce are all on the menu, as are these straightforward rhubarb bars.

A standby Rhubarb Bars

Sweet-tart flavor. Rhubarb desserts are all about balance because without that, rhubarb is so tart it’s practically inedible! These rhubarb bars add enough sugar (and strawberry jam!) to make the rhubarb palatable without completely drowning out that pop of tartness.

Layers of deliciousness. The rhubarb bars begin with a buttery oat crust that’s spiced with cinnamon. The jammy fruit layer goes over the crust, then a sprinkling of crumble goes on top for the reliable finishing touch.

Straightforward to mix. If preparing pie crust from scratch gives you heart palpitations, you’ll love these simple rhubarb bars. Simmer the filling on the stovetop, mix the crust and topping (the same mixture is used for both!), layer, and bake. Like pie, you can serve the bars à la mode for a scrumptious dessert.

What goes in

• Granulated Sugar: We add just enough to take the sour edge off the the rhubarb.
• Cornstarch: Cornstarch is commonly used to thicken sauces. Look for it in the baking aisle.
• Rhubarb: The star of the show! If you’re using fresh, remember to discard the leaves. The stalks are edible but the leaves are not. Choose stalks that are smaller in size (larger than two inches wide and they’re likely to be stringy), firm, and free of blemishes. The color of rhubarb can vary from deep red to green. The flavor is the same, no matter the color.
• Strawberry Jam: Strawberries and rhubarb are often paired together because they’re both in season at the same time and because the sweet berries bring balance to the rhubarb. Here, we keep it straightforward by using jam.
• Speedy Oats: Speedy oats are chopped small to cook more quickly. If you have rolled oats (or old-fashioned oats) on hand, you can use those for the crust instead of speedy oats. Simply give them a blitz in the food processor first.
• All-Purpose Flour: Lightly spoon the flour into the measuring cup, then level off the excess with a straight edge.
• Light Brown Sugar: Light brown sugar brings a note of caramel to the crust, without the more assertive molasses flavor of dark brown sugar.
• Ground Cinnamon: The warmth of cinnamon is the reliable addition to bring everything together.
• Salt: A pinch of salt keeps the crust from tasting bland or flat.
• Unsalted Butter: Let the butter soften to room temperature so you’ll be able to work it into the other crust ingredients.

Cooking Tip

When fresh rhubarb isn’t in season, you can use frozen. Note that frozen rhubarb may take a little more time to break down on the stovetop if you don’t thaw it first. Frozen rhubarb is featured in our photos.

How it comes together

Prep. Preheat your oven to 325°F. Coat a 9 x 13 inch baking dish with cooking spray, add a layer of parchment paper, then spray the parchment paper. (The first spritz of cooking spray helps keep the parchment paper from sliding.)

Make the rhubarb filling. Combine the sugar and cornstarch in a small saucepan, then stir in the remaining filling ingredients. Turn the heat on to medium and bring to a simmer, stirring constantly. Reduce the heat to medium-low and continue to cook until the rhubarb is broken down and the mixture is thick. Set aside to cool.

Mix crust ingredients. Stir together all of the crust ingredients except the butter in a mixing bowl, then cut in the butter until the mixture is crumbly and holds together when pinched between two fingers. Use a fork, a pastry cutter, or your fingers to cut in the butter.

Make bottom crust. Reserve 2 cups of the crumb mixture and press the rest into the baking dish. Bake the crust for 10 minutes.

Add filling and top crust. Spoon the filling over the crust, then sprinkle the reserved crumb mixture over the top, patting it down gently with a large spoon. Bake for 50 minutes more.

Cool before slicing. Let the bars cool completely (they’ll be delicate when still warm!), then lift them from the pan using the parchment paper and transfer to a cutting board. Cut with a sharp knife, then serve.

Ways to change it

• Switch up the jam. Instead of strawberry jam, try raspberry jam. Blueberries, blackberries, and peaches are also unexpectedly rich pairings with rhubarb.
• Swap cardamom for the cinnamon. Cardamom has a distinctive flavor that’s more complex than cinnamon; it’s a popular spice in Scandinavian cooking and baking.
• Rather have cake? Try our coffee cake-style rhubarb cake, which features a crunchy streusel topping. It’s so good (and it’s straightforward to mix!).

Make Ahead Ideas

You can make the rhubarb filling up to 2 days in advance. Store it in the refrigerator in an airtight container. If it’s too thick to spread when you take it out of the fridge, warm it up a bit in the microwave or allow it to come to room temperature.

Keeping leftovers

Store these rhubarb bars in an airtight container at room temperature for 4 to 5 days, or in the refrigerator for up to 7 days.

To freeze, wrap each bar in plastic wrap and then in foil. Transfer the bars to a freezer-friendly bag or container and freeze for up to 3 months. Thaw overnight in the fridge or set them on the counter until they come to room temperature.

• Yield: 24 bars
• Prep: 15 minutes
• Cook: 1 hour
• Total: 2 hours 15 minutes

Ingredients

For the Filling:

• ½ cup granulated sugar
• ¼ cup cornstarch
• 4 cups chopped rhubarb, fresh or frozen (see note)
• ¼ cup strawberry jam
• ⅓ cup water

For the Bars:

• 2 cups quick oats
• 2 cups all-purpose flour
• 1 ¼ cups light brown sugar, firmly packed
• 1 teaspoon ground cinnamon
• ½ teaspoon salt
• 1 cup unsalted butter, softened ( 2 sticks)

Method

1. Preheat oven to 325°F. Spray a 9 × 13-inch baking pan or dish lightly with nonstick cooking spray. LIne with parchment paper, spray again.
2. For the filling: In a small saucepan, mix together sugar and cornstarch. Add rhubarb, jam, and water. Stir to combine. Bring to a simmer over medium heat, stirring constantly. Reduce heat to medium low and continue to cook until thickened and rhubarb is mostly broken down, 10 minutes, or longer if the rhubarb is frozen. Mixture will be very thick. You should have about 2 ½ cups of filling. Set aside to cool slightly.
3. For the bars: In a large mixing bowl, combine oats, flour, brown sugar, cinnamon, and salt. Add butter and use a pastry cutter or two forks or knives to cut in the butter until the mixture is well-mixed and crumbly. It should hold together when you press it with your fingers.
4. Set aside 2 cups of crumb mixture. Put the remaining crumb mixture into the prepared pan and press down firmly in an even layer, using your fingers or the back of a large spoon. Bake for 10 minutes.
5. Remove pan from oven and carefully spoon fruit filling evenly over crust. Sprinkle with reserved crumb mixture and gently pat down with a large spoon. Put the bars back in the oven and bake for 50 minutes or until golden brown.
6. Cool completely. Using the parchment paper as handles, lift the bars from the pan and set on a cutting board. Using a large sharp knife, cut the bars into the desired size.

Notes

Rhubarb: If you buy frozen rhubarb, you’ll need about 21 oz. After testing this recipe, we found that fresh rhubarb works better than purchased frozen rhubarb which seems less juicy. If you freeze your own rhubarb, that works great, too.

Storage: Store bars in an airtight container for 4 to 5 days. If you want to keep them longer, refrigerate the bars for up to 7 days. To freeze the bars, wrap each bar individually in plastic wrap and then in foil. Transfer the wrapped bars into a freezer-friendly bag or container for up to 3 months. Thaw them overnight in the fridge or set them on the counter until they come to room temperature.

Recipe retested and revised 3/2024. Previously Rhubarb Cardamom Shortbread Bars. If desired, swap cardamom for the cinnamon in this recipe. Use 1 teaspoon ground cardamom instead of ground cinnamon.