Baking Desserts Snacks strawberry rhubarb crumble bars spring fruit

Strawberry Rhubarb Crumble Bar

Name: Strawberry Rhubarb Crumble Bar
Prep time: 20 min
Cook time: 35 min
Total time: 55 min
Yield: 8 servings
Cuisine: American
Ingredients: 1 cup all-purpose flour; 1 cup old-fashioned rolled oats; 0.75 cup light brown sugar (loosely packed); 1 pinch fine sea salt; 0.5 cup salted butter, melted; 2 cups fresh strawberries, hulled and quartered; 1.5 cups fresh rhubarb, trimmed and chopped; 0.333 cup granulated sugar (adjust to taste); 1.5 tablespoons cornstarch; 1 tablespoon fresh lemon juice

Bright, tangy strawberry-rhubarb filling is sandwiched between a buttery oat-crumble base and crunchy oat topping for an irresistible bar. These bake in a single 8x8 pan and are perfect for spring gatherings, potlucks, or an easy make-ahead dessert.

0.0(0 reviews)

Prep: 20m · Cook: 35m · Total55 mins

DifficultyEasy

Serves8

AuthorSara

Sara's note

"These bars balance bright, tart rhubarb with sweet strawberries and a buttery oat crumble—great warmed with a scoop of vanilla ice cream or chilled and packed for a picnic. Home bakers will love how reliably the filling sets after chilling, making clean slices every time."

Strawberry Rhubarb Crumble Bar

Bright, tangy strawberry and rhubarb meet a satisfyingly buttery oat crumble in these single-pan bars—an easy way to capture spring flavors without fuss. The dual oat layers are what make this version sing: old‑fashioned oats in the base provide chew and structure so the bars hold together, while reserving a portion of the crumble for the topping creates textural contrast and lets the filling bubble up through golden pockets. A short par-bake firms the crust so the fruit juices don’t turn it into mush, and a judicious amount of cornstarch plus a squeeze of lemon keeps the filling glossy and balanced against the rhubarb’s natural tartness.

This recipe is written for home bakers who want an impressive but low-stress dessert for potlucks, picnics, or a weeknight treat—make it the day before to get clean slices and deeper flavor. Because the recipe uses simple pantry items and minimal hands-on time, it’s forgiving to small substitutions (gluten‑free oats, a touch of ginger, or coconut oil for a vegan spin). Slice them cold for tidy squares, or warm a piece and serve with vanilla ice cream for a softer, more decadent presentation.

Plan your timing

Enter your target meal time:

6:01 pm–6:10 pm→Make the oat-crumble base and reserve topping

6:10 pm–6:19 pm→Prepare the strawberry-rhubarb filling

6:19 pm–6:28 pm→Assemble the bars

6:28 pm–6:37 pm→Top with reserved crumble

6:37 pm–6:46 pm→Bake until bubbling and golden

6:46 pm–6:55 pm→Cool, chill, and slice

Ingredients

Yield

Instructions

Make the oat-crumble base and reserve topping

Preheat oven to 350°F (175°C) and line an 8x8-inch square pan with parchment, leaving an overhang. In a medium bowl combine flour, rolled oats, light brown sugar, and a pinch of salt; stir to mix. Pour in the melted butter and stir until the mixture holds together when pressed; set aside about 1 to 1¼ cups of this mixture for the topping, then press the remaining mixture firmly and evenly into the prepared pan. Par-bake the crust for 10–12 minutes, until just set and beginning to turn golden.

For this step

1 cupall-purpose flour
1 cupold-fashioned rolled oats
0.75 cuplight brown sugar (loosely packed)
1 pinchfine sea salt
0.5 cupsalted butter, melted

Make the oat-crumble base and reserve topping

Prepare the strawberry-rhubarb filling

While the crust par-bakes, toss the strawberries and rhubarb with granulated sugar, cornstarch, and lemon juice in a bowl until evenly coated. Let the fruit sit 5–10 minutes to macerate; if the fruit is very juicy, you can increase cornstarch by 1 teaspoon. Taste and add a little more sugar if desired—the rhubarb can be quite tart.

For this step

2 cupsfresh strawberries, hulled and quartered
1.5 cupsfresh rhubarb, trimmed and chopped
0.38 cupgranulated sugar (adjust to taste)
1.5 tablespoonscornstarch
1 tablespoonfresh lemon juice

Assemble the bars

Spread the macerated strawberry-rhubarb mixture evenly over the warm, par-baked crust, gently pressing any large pieces so the layer is compact. If there is excess liquid at the bottom of the bowl, spoon mostly the fruit and thickened juices into the pan to avoid a soggy crust.

Top with reserved crumble

Evenly sprinkle the reserved oat-crumble mixture over the fruit layer, breaking up any large clumps so the topping is slightly lumpy and allows the filling to bubble through. Lightly press a few spots so the topping contacts the filling but remains textured.

Bake until bubbling and golden

Return the pan to the oven and bake 22–28 minutes, until the fruit filling is bubbling in the center and the topping is golden brown. If the topping browns too quickly, tent loosely with foil for the last 5–10 minutes.

Cool, chill, and slice

Allow the bars to cool on a wire rack until they reach room temperature, then chill in the refrigerator at least 2 hours (overnight is best) to fully set the filling. Use the parchment overhang to lift the slab from the pan and slice into 8 bars with a sharp knife, wiping the knife between cuts for clean edges.

Tips from the kitchen

Par‑bake the crust

Par‑baking for 10–12 minutes sets the base so the fruit layer won’t make it soggy; press the crust firmly and evenly into the pan for a stable bar that slices cleanly.

Reserve the topping

Set aside 1 to 1¼ cups of the crumble before pressing the base; this keeps the topping lighter and allows the fruit to peek through when it bakes.

Adjust cornstarch carefully

If your fruit is very juicy, add an extra teaspoon of cornstarch to prevent a runny filling, but avoid over‑thickening which can make the filling gummy.

Macerate briefly

Let the strawberries and rhubarb sit with sugar and lemon for 5–10 minutes to draw out juices and dissolve the sugar so the cornstarch can thicken evenly.

Chill before slicing

Refrigerate at least 2 hours (overnight is best) so the filling fully sets; use a hot, sharp knife and wipe between cuts for neat squares.

Variations & substitutions

Gluten‑free swap

Use certified gluten‑free rolled oats and replace the all‑purpose flour with an equal amount of almond flour or a 1:1 gluten‑free baking flour for a similar texture.

Vegan version

Substitute melted coconut oil or vegan butter for the butter and use brown sugar; chilling slightly longer helps the filling set since coconut oil is softer at room temperature.

Spice & flavor twist

Stir 1 teaspoon of grated fresh ginger or ½ teaspoon ground cardamom into the filling for warmth, or add 1 teaspoon vanilla extract to the fruit for a rounder flavor.

Other fruit combinations

Swap strawberries and rhubarb for equal parts raspberries and rhubarb, or peaches and rhubarb (use slightly more cornstarch with very juicy peaches) for seasonal variations.

Storage & make-ahead

Store cooled bars in an airtight container in the refrigerator for up to 4–5 days; chilling improves sliceability and flavor. For longer storage, wrap the slab tightly in plastic and foil and freeze for up to 2 months, thawing overnight in the fridge. Reheat individual portions briefly in a 300°F oven for 8–12 minutes to revive the topping, or microwave for 20–30 seconds for a warmed serving (the crust may soften).

What to serve with it

Serve chilled squares with a dollop of slightly tangy crème fraîche, whipped cream, or a scoop of vanilla ice cream that contrasts the tart rhubarb. Pair with a light tea, an americano, or a sparkling rosé for a springtime gathering, and consider a dusting of powdered sugar or a few fresh sliced strawberries on top for a pretty finish.

Frequently asked questions

Can I use frozen strawberries and rhubarb?

Yes—use frozen fruit straight from the freezer and increase cornstarch by about 1–2 teaspoons because frozen fruit releases more water as it thaws and bakes; no need to thaw first.

Why is my crust soggy on the bottom?

A soggy bottom usually means the crust was under‑par‑baked or the fruit layer had excess liquid; press the base firmly, par‑bake until just golden, and spoon mostly fruit (not excess juices) into the pan.

How can I tell when the filling is done?

Look for the filling to be actively bubbling in the center and the topping to be golden brown; bubbling indicates the cornstarch has been activated and the filling is thickening.

Can I make these ahead of time?

Absolutely—these are better after chilling overnight, which firms the filling and makes slicing cleaner; store refrigerated and bring to room temperature or gently rewarm before serving if desired.

Can I replace cornstarch with something else?

You can use an equal amount of arrowroot powder for a clearer, glossy finish, or 1½ times the amount of tapioca starch; avoid flour, which can leave a pasty texture.

About the author

Sara See all recipes by Sara →

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Ingredients

8 servings

Step 1: Make the oat-crumble base and reserve topping

all-purpose flour1 cup
old-fashioned rolled oats1 cup
light brown sugar (loosely packed)0.75 cup
fine sea salt1 pinch
salted butter, melted0.5 cup

Step 2: Prepare the strawberry-rhubarb filling

fresh strawberries, hulled and quartered2 cups
fresh rhubarb, trimmed and chopped1.5 cups
granulated sugar (adjust to taste)0.38 cup
cornstarch1.5 tablespoons
fresh lemon juice1 tablespoon

Nutrition Facts

Per serving: 1 bar (130g)

Calories320

Total Fat14g

Saturated Fat8g

Trans Fat0g

Polyunsaturated Fat1.5g

Monounsaturated Fat3g

Total Carbohydrates44g

Dietary Fiber3g

Total Sugars22g

Protein3g

Nutrition values are estimated from USDA ingredient data and may vary based on preparation, brands, and portion sizes. Values are provided for informational purposes only.

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