These lemon rhubarb bars combine a sweet-tart lemon custard studded with vibrant rhubarb, a buttery shortbread base, and a lightly toasted Swiss meringue topping. They’re a bright, seasonal treat that celebrates rhubarb when it first appears in spring.
Rhubarb signals spring for me the way citrus signals winter: its short season makes every appearance special. Those first bright pink and red stalks arrive at the same time fruit trees burst into bloom, and I try to use them while they’re available. I’ve worked rhubarb into cakes, tarts, and pies before, and these bars are my take on old-fashioned rhubarb custard bars with a lively lemon twist and a clean shortbread base.
Rather than calling them strictly lemon bars or rhubarb custard bars, this recipe blends both: the custard gets three sources of lemon flavor—freshly squeezed lemon juice, lemon zest, and a touch of lemon oil—plus a generous amount of diced rhubarb. The result is a vivid, balanced dessert: buttery shortbread, a sweet lemon custard, tangy rhubarb, and a sweet, toasty Swiss meringue that brings everything together.
Ingredients
* See recipe card for the full ingredient list and exact quantities.
Unsalted butter – Use unsalted butter so you can control the amount of salt in the bars.
Lemon oil – A small amount of lemon oil adds concentrated citrus aroma and amplifies the fresh lemon juice and zest in the custard.
The Swiss meringue topping
I use Swiss meringue for the topping because it’s smoother and more stable than many other meringues. It holds its shape well, and when made correctly it doesn’t weep in the fridge. While the bars are best eaten fresh, leftover bars with meringue have kept in the refrigerator for several days without issue.
Easy spreading or decorative piping?
This recipe makes enough meringue to fully cover the bars, but you can apply it in two ways depending on the look you want:
- Spread a full layer: The simplest approach. It hides the rhubarb color but gives every bite a perfect amount of sweet meringue.
- Pipe decorative swirls: Piping preserves the rhubarb’s pink color and creates an elegant presentation. If you pipe, you may have some leftover meringue.
How to use leftover meringue
Use leftover meringue to make crunchy meringue kisses:
- Pipe small swirls onto a parchment-lined sheet, leaving space between each.
- Bake at 200°F (93°C) for 60–90 minutes until dry to the touch and easily lifted from the paper.
- Turn the oven off and let them cool inside to avoid cracking.
Equipment
8-inch square metal baking pan – A square pan with sharp corners helps produce clean, professional-looking bars.
Large piping bag – Useful if you choose to pipe decorative meringue swirls onto each bar.
Piping tip – A St. Honoré tip or any large decorative tip works well for dramatic swirls.
If you pipe and end up with extra meringue, bake it into kisses at low temperature to avoid waste.
Frequently asked questions
These bars are best eaten fresh. Store extras in the refrigerator in a single layer in an airtight container for up to 5 days. Custard-based desserts often separate and become watery if frozen, so freezing is not recommended.
Rinse stalks to remove dirt and trim off any leafy tops. Rhubarb leaves contain oxalic acid and should not be eaten. If stalks are thick, split them lengthwise, then dice into even thumbnail-sized pieces so they cook evenly. Early forced rhubarb is often thinner and may not need splitting.
More rhubarb recipes
-
Strawberry Rhubarb Panna Cotta Tart
-
Rhubarb Frangipane Tart
-
Strawberry Rhubarb Slab Pie
-
Cherry Rhubarb Pie
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📖 Recipe
Lemon Rhubarb Bars
INGREDIENTS
Shortbread crust
- 113 grams unsalted butter, chilled and cubed
- 50 grams granulated sugar
- 120 grams all-purpose flour
- ¼ teaspoon kosher salt
Lemon rhubarb custard layer
- 23 grams all-purpose flour
- 150 grams (¾ cup) granulated sugar
- 2 large eggs, beaten
- 60 mL heavy cream
- lemon zest from 1 large lemon
- 60 mL freshly squeezed lemon juice (same lemon)
- 2.5 mL lemon oil
- 366 grams rhubarb, diced
Swiss meringue topping
- 100 grams egg whites (~3 large whites)
- 150 grams granulated sugar
- 1.25 mL vanilla extract
INSTRUCTIONS
Shortbread layer
- Preheat the oven to 350°F (177°C).
- Line an 8-inch square pan with parchment, leaving flaps on two opposite sides to lift the bars out later.
- In a stand mixer fitted with the paddle attachment, combine butter, sugar, flour, and salt and mix until the dough comes together with a sandy texture.
- Press the dough evenly into the prepared pan. Cover with plastic wrap and use the flat bottom of a glass or measuring cup to firmly pack and smooth the crust. Chill for 30 minutes.
- Bake 10–12 minutes until the crust loses its shine and just begins to color. Cool on a rack.
Lemon rhubarb custard layer
- Whisk together the flour and sugar in a large bowl.
- Add the beaten eggs and whisk to combine.
- Stir in the heavy cream, zest, lemon juice, and lemon oil until smooth.
- Fold in the diced rhubarb and pour the mixture over the cooled shortbread. Tap the pan on the counter to remove air bubbles.
- Bake at 350°F (177°C) for 40–45 minutes until the custard is fully set and not jiggly. Cool on a rack, then refrigerate for at least 1 hour to set.
Swiss meringue topping
- Whisk egg whites, sugar, and vanilla in a small saucepan over low heat, stirring until warm and sugar dissolves (the mixture should feel smooth between your fingers or reach about 160°F if you use a thermometer).
- Transfer to a stand mixer with the whisk attachment and beat until stiff, glossy peaks form, about 5 minutes. The meringue should be thick and hold its shape.
- Remove fully chilled bars from the pan and place them on a metal baking sheet, discarding the parchment underneath.
- Option 1 — Spread: Scoop meringue over the cooled bars, spread evenly, and create swirls with an offset spatula. Torch the surface briefly to toast. Slice into 16 squares, wiping the knife clean between cuts.
- Option 2 — Pipe: Slice the bars into 16 squares first, then pipe meringue onto each piece using a piping bag fitted with a large decorative tip. Toast the meringue with a torch.
- Serve promptly. Store any extra bars in a single layer in an airtight container in the refrigerator.
EQUIPMENT
- 8-inch square baking pan
- Large piping bag (if piping)
- St. Honoré or similar large piping tip (optional)