Delicious Lemon Rhubarb Bars

Finding a dessert that perfectly balances sweet and tart flavors while still being simple enough for a weeknight treat can be tough. After all, most fruit desserts either require fancy techniques or end up being too sweet, and it’s even harder when you’re working with seasonal ingredients like rhubarb that have a short window of availability.

Luckily, these lemon rhubarb bars check all the boxes: they’re tangy yet satisfying, easy to make with a basic shortbread crust, and perfect for using up that fresh rhubarb from your garden or farmers market.

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What Kind of Rhubarb Should I Use?

Fresh rhubarb is your best bet for these bars, and you’ll find it in grocery stores during spring and early summer when it’s in season. The color of the stalks can range from deep red to pink to green, and while the red varieties look prettier, they all taste pretty similar so don’t worry too much about the color. Make sure to trim off any leaves if they’re still attached, as those are toxic and shouldn’t be eaten. If fresh rhubarb isn’t available, frozen rhubarb works just fine – just thaw it first and drain off any excess liquid so your bars don’t turn out soggy.

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Options for Substitutions

While these bars are pretty straightforward, here are a few swaps you can make if needed:

• Rhubarb: Fresh rhubarb is really the star here, so I’d recommend sticking with it if possible. If you absolutely must substitute, try using frozen rhubarb – just thaw it completely and drain any excess liquid before using.
• Butter: You can swap the butter for coconut oil in the crust for a dairy-free version. Use it in solid form and work it into the flour the same way you would with butter.
• Lemon juice and zest: Fresh lemon is best for that bright, tangy flavor, but bottled lemon juice will work in a pinch. For the zest, there’s no great substitute – it adds a lot of flavor, so try to use fresh lemons if you can.
• Eggs: The eggs are essential for the custard-like filling, so I wouldn’t recommend substituting them. They help the bars set properly and give them their texture.
• Flour: All-purpose flour works best here, but you can use a 1:1 gluten-free baking flour if needed. The texture might be slightly different, but the bars should still turn out well.

Watch Out for These Mistakes While Baking

The biggest mistake when making lemon rhubarb bars is underbaking the crust, which leads to a soggy bottom layer – make sure it’s lightly golden before adding the filling, not pale and soft.

Another common error is cutting the rhubarb pieces too large, causing them to release too much liquid and make the bars watery, so aim for pieces no bigger than half an inch.

Don’t skip cooling the bars completely before slicing, as cutting them while warm will result in messy, crumbly pieces that fall apart – patience here makes all the difference.

For extra insurance against sogginess, you can brush a thin layer of the egg mixture over the hot crust before adding the full filling, which creates a seal between the crust and topping.

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What to Serve With Lemon Rhubarb Bars?

These tangy bars are perfect on their own as a dessert or afternoon snack, but they’re even better with a dollop of freshly whipped cream or a scoop of vanilla ice cream to balance out the tartness. I love serving them alongside a hot cup of tea or coffee for a relaxing afternoon treat. They also work great as part of a dessert spread at potlucks or barbecues, especially during spring and early summer when rhubarb is in season. If you want to get fancy, dust them with a little powdered sugar right before serving to make them look extra nice.

Storage Instructions

Store: Keep your lemon rhubarb bars in an airtight container in the fridge for up to 5 days. They actually taste even better the next day once all 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. You can grab one whenever you need a sweet treat.

Serve: Let frozen bars thaw in the fridge overnight or at room temperature for about 30 minutes before serving. They’re delicious cold straight from the fridge, which makes them perfect for a refreshing dessert on warm days.

Estimated Nutrition

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

• Calories: 1950-2100
• Protein: 28-33 g
• Fat: 55-65 g
• Carbohydrates: 355-375 g

Ingredients

For the crust:

• 1 cup flour (I always use King Arthur all-purpose flour)
• 1/3 cup butter (cold and cut into 1/2-inch cubes)
• 1/4 cup sugar
• 1/4 tsp salt

For the filling:

• 2 cups rhubarb (sliced into 1/4-inch thick pieces)
• 3 eggs
• 1 1/4 cups sugar
• 1/2 cup flour
• 1/4 cup lemon juice (freshly squeezed for best flavor and acidity)
• 2 tbsp lemon zest
• 1/2 tsp vanilla extract

Step 1: Make and Bake the Shortbread Crust

• 1 cup flour
• 1/3 cup butter
• 1/4 cup sugar
• 1/4 tsp salt

Preheat your oven to 350°F.

In a bowl, combine the flour, sugar, and salt.

Add the cold butter cubes and work them into the flour using your fingertips or a pastry cutter until the mixture resembles coarse breadcrumbs—this keeps the crust tender and flaky.

Press this mixture firmly into the bottom of a 9×13 inch baking dish, creating an even layer.

Bake for 20 minutes until the crust is light golden and set.

I like to use King Arthur all-purpose flour here because it creates a more reliable, tender texture that won’t turn tough.

Step 2: Create the Lemon-Rhubarb Custard Base

• 1/4 cup lemon juice
• 1 cup rhubarb
• 3 eggs

While the crust bakes, prepare the filling.

Add the lemon juice, 1 cup of the sliced rhubarb, and the eggs to a bowl.

Using an immersion blender, blend until smooth and well combined—this creates a silky custard base and naturally incorporates the rhubarb juice for flavor and moisture.

The blender also ensures the eggs are fully emulsified, which helps the filling set properly.

Step 3: Finish the Filling and Assemble

• lemon-rhubarb mixture from Step 2
• 2 tbsp lemon zest
• 1 1/4 cups sugar
• 1/2 cup flour
• 1 cup rhubarb
• 1/2 tsp vanilla extract

To the lemon-rhubarb mixture from Step 2, stir in the lemon zest, sugar, and flour until just combined—this thickens the filling slightly and ensures even baking.

Gently fold in the remaining 1 cup of raw rhubarb slices and the vanilla extract.

For the best texture, I keep some rhubarb pieces whole rather than blending all of them, so you get pockets of tart fruit throughout the bars.

Pour this filling over the warm crust from Step 1, spreading it evenly.

Step 4: Bake and Cool

Bake at 350°F for 35 minutes, until the filling is set but still slightly jiggles in the very center—this means it will have a tender, custardy texture rather than becoming rubbery.

The edges should look set and slightly golden.

Let the bars cool completely in the pan at room temperature (about 1 hour), then refrigerate for at least 2 hours before cutting into squares.

Chilling helps them set properly and makes them easier to cut cleanly.