Classic Rhubarb Crumble Bars

I didn’t grow up eating rhubarb. My mom wasn’t really into those tart, tangy flavors, so it just never made it onto our table. When I first tried rhubarb pie at a friend’s house in my twenties, I couldn’t believe what I’d been missing.

The thing about rhubarb is that it needs sugar—and lots of it. That’s why it works so well in desserts. These rhubarb crumble bars are basically all my favorite parts of rhubarb pie, but way easier to make. No rolling out pie crust, no fancy crimping. Just press a simple dough into a pan, add the rhubarb filling, sprinkle on an oat topping, and bake. They’re perfect for potlucks because you can slice them into neat squares that people can grab with their hands.

What Kind of Rhubarb Should I Use?

Fresh rhubarb is always your best bet for these bars, and you’ll find it in grocery stores during spring and early summer. The color of the stalks doesn’t really matter – some rhubarb is bright red while others are more green or pink, and they all taste pretty similar. What you do want to look for are firm, crisp stalks without any soft spots or wilting. If fresh rhubarb isn’t available, you can use frozen rhubarb instead – just make sure to thaw it completely and drain off any excess liquid before using it in the recipe, otherwise your bars might turn out soggy.

Options for Substitutions

This recipe is pretty forgiving, so here are some swaps you can make if needed:

• Rhubarb: Fresh rhubarb is really the star here, but if it’s out of season, you can use frozen rhubarb – just thaw it first and drain any excess liquid before using. You could also try a mix of rhubarb and strawberries (about half and half) for a sweeter twist.
• Salted butter: If you only have unsalted butter on hand, just add a pinch of salt (about ¼ teaspoon) to the dough and crumble topping.
• Old-fashioned rolled oats: Quick oats can work in the crumble topping, though they’ll give you a slightly finer texture. Don’t use instant oats though – they’ll turn mushy.
• Vanilla sugar: Not everyone keeps vanilla sugar around. Just use regular sugar and add ½ teaspoon of vanilla extract to the melted butter instead.
• Lemon: The lemon really brightens up the rhubarb, but you can use lime or orange zest and juice if that’s what you have. The citrus helps balance the tartness.
• Cornstarch: You can swap this with the same amount of flour or tapioca starch to thicken the rhubarb filling.

Watch Out for These Mistakes While Baking

The biggest mistake when making rhubarb crumble bars is not cooking the rhubarb filling long enough, which can leave you with a watery mess that seeps into the crust – make sure to simmer it for the full 5 minutes after adding the cornstarch so it thickens properly.

Another common error is skipping the cooling step for the rhubarb filling before pouring it over the crust, as hot filling can make the bottom layer soggy instead of creating distinct layers.

Don’t press the crumble topping down too firmly when sprinkling it over the rhubarb – it should stay loose and crumbly to get that nice texture contrast.

Finally, resist the urge to cut these bars right out of the oven, since letting them cool completely allows the filling to set up and makes slicing much cleaner and easier.

What to Serve With Rhubarb Crumble Bars?

These rhubarb crumble bars are perfect on their own, but they really shine when you serve them with a scoop of vanilla ice cream or some fresh whipped cream on top. The cold, creamy topping balances out the tart rhubarb filling and makes for a great dessert. I also love pairing these bars with a hot cup of coffee or tea for an afternoon snack – the buttery crumble and tangy fruit go perfectly with something warm to drink. If you’re serving them for a party or potluck, try cutting them into smaller squares and dusting them with a bit of powdered sugar for a nice presentation.

Storage Instructions

Store: Keep your rhubarb crumble bars in an airtight container in the fridge for up to 5 days. The bars actually taste even better the next day once the flavors have had time to meld together, so don’t be afraid to make them ahead!

Freeze: These bars freeze really well for up to 3 months. Just cut them into individual portions, wrap each one in plastic wrap, and store them in a freezer-safe container or bag. You can grab one whenever you need a quick dessert or snack.

Serve: Let frozen bars thaw in the fridge overnight or at room temperature for about an hour. I like mine cold straight from the fridge, but you can also warm them up in the oven at 300°F for about 10 minutes if you prefer them warm with a scoop of vanilla ice cream.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 3100-3400
• Protein: 28-34 g
• Fat: 130-145 g
• Carbohydrates: 435-470 g

Ingredients

For the base:

• 1/2 cup sugar
• 2 cups all-purpose flour
• 1 tbsp baking powder
• 2/3 cup butter (cold and cut into 1/2-inch cubes)
• 1/2 teaspoon salt
• 1 egg

For the rhubarb filling:

• 5 stalks rhubarb (sliced into 1/2-inch thick pieces)
• 1/2 cup sugar
• 1 lemon (freshly zested and juiced)
• 1 teaspoon vanilla extract
• 2 1/2 tsp cornstarch

For the topping:

• 1 cup old fashioned oats
• 1/2 cup sugar
• 1 tsp vanilla sugar
• 1/2 teaspoon ground cinnamon
• 1/2 cup butter (melted and cooled slightly)

Step 1: Prepare the Base Layer and Mise en Place

• 5 stalks rhubarb, sliced into 1/2-inch pieces
• 1 lemon, zested and juiced

Preheat your oven to 400°F and grease a 9×13 inch baking dish.

While the oven heats, gather all your ingredients and prepare them for cooking.

Slice the rhubarb into 1/2-inch thick pieces and set aside.

Zest and juice the lemon, keeping them separate.

Cut the cold butter into 1/2-inch cubes for the base layer—keeping the butter cold is key to creating that tender, crumbly crust.

Step 2: Make and Press the Base Crust

• 2 cups all-purpose flour
• 1 tbsp baking powder
• 1/2 teaspoon salt
• 2/3 cup cold butter, cut into 1/2-inch cubes
• 1 egg
• 1/2 cup sugar

In a medium bowl, whisk together the flour, baking powder, and salt for the base.

Add the cold butter cubes and mix with your fingertips until the mixture resembles coarse breadcrumbs—this texture is what creates that tender crumb.

Stir in the egg and 1/2 cup sugar until just combined.

Press this mixture firmly into the bottom of your prepared baking dish, creating an even layer.

I like to use the bottom of a measuring cup to pack it down smoothly, which helps it hold together when you add the filling.

Step 3: Cook and Thicken the Rhubarb Filling

• rhubarb from Step 1
• 1/2 cup sugar
• lemon zest and juice from Step 1
• 2 1/2 tsp cornstarch

In a large saucepan over medium-high heat, combine the sliced rhubarb from Step 1 with 1/2 cup sugar, lemon zest, and lemon juice.

Stir occasionally and let it bubble for about 3-4 minutes until the rhubarb softens and releases its juices.

Sprinkle the cornstarch over the mixture while stirring constantly, then simmer for another 5 minutes until the filling thickens and becomes glossy.

This prevents a soggy bar by absorbing excess moisture from the rhubarb.

Step 4: Assemble and Top the Bars

• rhubarb filling from Step 3
• 1 cup old fashioned oats
• 1/2 cup sugar
• 1 tsp vanilla sugar
• 1/2 teaspoon ground cinnamon
• 1/2 cup butter, melted and cooled slightly
• 1 teaspoon vanilla extract

Remove the rhubarb filling from heat and let it cool for 5 minutes—this prevents the filling from overcooking the delicate base.

While it cools, prepare the topping by combining the oats, 1/2 cup sugar, vanilla sugar, cinnamon, and melted butter in a small bowl until everything is evenly coated.

Pour the cooled rhubarb filling over the base crust from Step 2, spreading it gently into an even layer.

Sprinkle the crumble topping evenly over the filling, pressing it down slightly so it doesn’t blow around in the oven.

I find that sprinkling it in sections and gently pressing as I go creates a more cohesive topping.

Step 5: Bake and Cool

Bake the assembled bars at 400°F for 20-25 minutes until the topping is golden brown and the filling bubbles slightly around the edges—you’ll see a few small bubbles peeking through the crumble.

Let the pan cool on a wire rack for at least 15-20 minutes before cutting into squares.

This cooling time allows the filling to set and the bars to hold their shape when you slice them.

Classic Rhubarb Crumble Bars

Delicious Classic Rhubarb Crumble Bars recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 20 minutes mins

Cook Time 35 minutes mins

Total Time 57 minutes mins

Servings: 16 bars

Calories: 3250

Ingredients Method

Ingredients

  

For the base

• 1/2 cup sugar
• 2 cups all-purpose flour
• 1 tbsp baking powder
• 2/3 cup butter (cold and cut into 1/2-inch cubes)
• 1/2 teaspoon salt
• 1 egg

For the rhubarb filling

• 5 stalks rhubarb (sliced into 1/2-inch thick pieces)
• 1/2 cup sugar
• 1 lemon (freshly zested and juiced)
• 1 teaspoon vanilla extract
• 2 1/2 tsp cornstarch

For the topping

• 1 cup old fashioned oats
• 1/2 cup sugar
• 1 tsp vanilla sugar
• 1/2 teaspoon ground cinnamon
• 1/2 cup butter (melted and cooled slightly)

Method

 

1. Preheat your oven to 400°F and grease a 9x13 inch baking dish. While the oven heats, gather all your ingredients and prepare them for cooking. Slice the rhubarb into 1/2-inch thick pieces and set aside. Zest and juice the lemon, keeping them separate. Cut the cold butter into 1/2-inch cubes for the base layer—keeping the butter cold is key to creating that tender, crumbly crust.
2. In a medium bowl, whisk together the flour, baking powder, and salt for the base. Add the cold butter cubes and mix with your fingertips until the mixture resembles coarse breadcrumbs—this texture is what creates that tender crumb. Stir in the egg and 1/2 cup sugar until just combined. Press this mixture firmly into the bottom of your prepared baking dish, creating an even layer. I like to use the bottom of a measuring cup to pack it down smoothly, which helps it hold together when you add the filling.
3. In a large saucepan over medium-high heat, combine the sliced rhubarb from Step 1 with 1/2 cup sugar, lemon zest, and lemon juice. Stir occasionally and let it bubble for about 3-4 minutes until the rhubarb softens and releases its juices. Sprinkle the cornstarch over the mixture while stirring constantly, then simmer for another 5 minutes until the filling thickens and becomes glossy. This prevents a soggy bar by absorbing excess moisture from the rhubarb.
4. Remove the rhubarb filling from heat and let it cool for 5 minutes—this prevents the filling from overcooking the delicate base. While it cools, prepare the topping by combining the oats, 1/2 cup sugar, vanilla sugar, cinnamon, and melted butter in a small bowl until everything is evenly coated. Pour the cooled rhubarb filling over the base crust from Step 2, spreading it gently into an even layer. Sprinkle the crumble topping evenly over the filling, pressing it down slightly so it doesn't blow around in the oven. I find that sprinkling it in sections and gently pressing as I go creates a more cohesive topping.
5. Bake the assembled bars at 400°F for 20-25 minutes until the topping is golden brown and the filling bubbles slightly around the edges—you'll see a few small bubbles peeking through the crumble. Let the pan cool on a wire rack for at least 15-20 minutes before cutting into squares. This cooling time allows the filling to set and the bars to hold their shape when you slice them.