Strawberry Rhubarb Crumble Bars with Buttery Shortbread

Quick Recipe Version (TL;DR)

• Yield: 16 bars
• Prep Time: 25 minutes
• Cook Time: 45 minutes
• Total Time: 1 hour 30 minutes (including cooling time)

Quick Ingredients

• 2 1/4 cups (280 g) all-purpose flour
• 1 cup (100 g) old-fashioned rolled oats
• 3/4 cup (150 g) granulated sugar, plus 2/3 cup (135 g) for filling
• 1/2 cup (100 g) packed light brown sugar
• 1 cup (225 g) unsalted butter, melted and slightly cooled
• 2 cups (about 250 g) diced strawberries
• 2 cups (about 250 g) diced rhubarb
• 2 tbsp cornstarch
• 2 tbsp fresh lemon juice + 1 tsp lemon zest
• 1 1/2 tsp vanilla extract, 1/2 tsp ground cinnamon, 1/2 tsp fine sea salt

Do This

• 1. Preheat oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang.
• 2. Stir flour, oats, granulated and brown sugars, salt, and cinnamon. Mix in melted butter and vanilla until crumbly.
• 3. Press about 2/3 of the mixture firmly into the pan for the base. Bake 15 minutes.
• 4. While crust bakes, toss strawberries, rhubarb, 2/3 cup sugar, cornstarch, lemon juice, lemon zest, and a pinch of salt.
• 5. Spread fruit filling evenly over hot crust. Crumble remaining dough over the top.
• 6. Bake 30–35 minutes, until topping is golden and filling is bubbling around edges.
• 7. Cool completely (at least 1 hour) in pan, then lift out with parchment and slice into bars.

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Why You’ll Love This Recipe

• Perfect balance of sweet strawberries and tart rhubarb, tucked between buttery, cookie-like layers.
• One dough does double duty for both the shortbread base and the crumb topping, making prep simple.
• Bars slice beautifully, travel well, and are ideal for picnics, potlucks, brunch, or afternoon coffee.
• Easy to customize with frozen fruit, spices, or nuts while still being very beginner-friendly.

Grocery List

• Produce: Fresh strawberries, fresh rhubarb, lemons
• Dairy: Unsalted butter
• Pantry: All-purpose flour, old-fashioned rolled oats, granulated sugar, light brown sugar, cornstarch, vanilla extract, ground cinnamon, fine sea salt, nonstick spray or extra butter for the pan (optional)

Full Ingredients

For the buttery shortbread base and crumb topping

• 2 1/4 cups (280 g) all-purpose flour
• 1 cup (100 g) old-fashioned rolled oats
• 3/4 cup (150 g) granulated sugar
• 1/2 cup (100 g) packed light brown sugar
• 1/2 tsp fine sea salt
• 1/2 tsp ground cinnamon (optional but recommended)
• 1 cup (225 g) unsalted butter, melted and slightly cooled (but still pourable)
• 1 1/2 tsp pure vanilla extract

For the strawberry-rhubarb filling

• 2 cups (about 250 g) fresh strawberries, hulled and chopped into 1/2-inch pieces
• 2 cups (about 250 g) fresh rhubarb, trimmed and chopped into 1/2-inch pieces
• 2/3 cup (135 g) granulated sugar
• 2 tbsp cornstarch
• 2 tbsp fresh lemon juice (from about 1 small lemon)
• 1 tsp finely grated lemon zest
• 1/4 tsp fine sea salt
• 1/2 tsp pure vanilla extract (optional, for extra aroma)

For the pan (optional but helpful)

• Butter or nonstick cooking spray (to lightly grease the pan under the parchment)
• Parchment paper (to create a sling for easy removal)

Step-by-Step Instructions

Step 1: Prep the pan and preheat the oven

Preheat your oven to 350°F (175°C) with a rack in the middle position. Lightly butter or spray an 8-inch square baking pan. Line the bottom and two opposite sides with a sheet of parchment paper, leaving a 2–3 inch overhang on the sides to create a sling. This will make it easy to lift the bars out later for neat slicing. If your parchment tends to curl, dab a tiny bit of butter underneath the corners to help it stick in place.

Step 2: Make the shortbread crumble mixture

In a large mixing bowl, combine the flour, oats, 3/4 cup granulated sugar, brown sugar, salt, and cinnamon. Stir with a whisk or fork until everything is evenly mixed and there are no lumps of sugar.

Pour in the melted butter and vanilla extract. Use a spatula or wooden spoon to stir until the mixture looks evenly moistened and forms clumps when you squeeze it in your hand. It should look like a cross between cookie dough and coarse crumbs, not like a smooth batter.

Step 3: Press and par-bake the crust

Scoop out about 2/3 of the crumble mixture (roughly 3 firmly packed cups) and transfer it to the prepared pan. Set the remaining 1/3 aside for the topping.

Press the mixture firmly and evenly into the bottom of the pan to form the shortbread base. Take your time here: use your fingertips, the flat bottom of a measuring cup, or a glass to press it into an even, compact layer without loose crumbs. This helps the crust hold together as a bar instead of crumbling.

Bake the crust for 15 minutes, until it is just starting to turn a very light golden color around the edges. While the crust par-bakes, prepare the fruit filling.

Step 4: Make the strawberry-rhubarb filling

In a medium bowl, combine the chopped strawberries, chopped rhubarb, 2/3 cup granulated sugar, cornstarch, lemon juice, lemon zest, salt, and vanilla extract (if using). Toss gently but thoroughly until all of the fruit is coated and no dry patches of cornstarch remain at the bottom of the bowl.

The mixture will look a bit dusty at first, then start to look glossy as the fruit releases some juice. Stir again just before using to redistribute the juices and cornstarch. This combination is what thickens the filling into a jammy layer as it bakes.

Step 5: Layer the filling and crumble topping

When the crust has finished its initial bake, remove the pan from the oven but leave the oven on. Give the fruit one last stir, then gently spoon it over the hot crust. Spread it into an even layer, making sure the fruit reaches all the way to the corners. Scrape any juices from the bowl over the top; you want all that flavor in your bars.

Take the remaining 1/3 crumble mixture and sprinkle it evenly over the fruit. Let some pieces stay in larger clumps and some in smaller crumbs for texture. There is no need to press it down; it will settle slightly as it bakes.

Step 6: Bake until bubbly and golden

Return the pan to the oven and bake for 30–35 minutes, or until the crumble topping is a rich, golden brown and the fruit filling is bubbling thickly around the edges. The center may still bubble a bit, but it should not look watery.

If the topping is browning too quickly before the filling is bubbling, tent the pan loosely with a piece of foil and continue baking until the filling looks thick and jammy.

Step 7: Cool completely, slice, and serve

Remove the pan from the oven and set it on a wire rack. Let the bars cool completely in the pan, at least 1 hour, but ideally 2–3 hours. This cooling time allows the fruit layer to set so the bars slice cleanly instead of oozing.

Once cool, use the parchment sling to lift the entire slab out of the pan and place it on a cutting board. Use a large, sharp knife to cut into 16 small bars (4 by 4 grid) or 9 larger bars. Wipe the knife with a warm, damp cloth between cuts for the neatest edges.

Serve at room temperature, or slightly chilled if you prefer a firmer texture. These are lovely on their own, but also wonderful with a spoonful of softly whipped cream or a small scoop of vanilla ice cream.

Pro Tips

• Do not skip the parchment sling. It makes lifting and slicing the bars so much easier and keeps the corners from sticking.
• Chop the fruit evenly. Aim for 1/2-inch pieces so the strawberries and rhubarb cook at the same rate and give you a uniform, jammy layer.
• Cool completely before cutting. The filling continues to set as it cools. If you cut too early, you will get tasty but messy squares.
• Adjust sweetness to taste. If your rhubarb is very tart or your strawberries are not very sweet, you can add an extra 1–2 tbsp sugar to the filling.
• Use weight measurements if possible. Measuring flour and oats by grams gives the best texture and avoids a dry or overly dense crust.

Variations

• Mixed-Berry Rhubarb Bars: Swap half of the strawberries for blueberries or raspberries. Keep the total fruit amount the same and use the same sugar and cornstarch ratios.
• Nutty Crumble Topping: Stir 1/2 cup chopped toasted almonds, pecans, or walnuts into the reserved crumble mixture before sprinkling it over the fruit.
• Warm Spice Version: Add 1/4 tsp ground ginger and an extra 1/2 tsp cinnamon to the crumble, and a pinch of cardamom to the filling for a cozy spiced twist.

Storage & Make-Ahead

Once completely cooled and sliced, store the bars in an airtight container, with parchment or wax paper between layers if stacking.

At cool room temperature, they keep well for up to 2 days. For longer storage, refrigerate for up to 5 days. The texture of the crust will gradually soften in the fridge, but the flavor remains excellent.

To freeze, place sliced bars on a parchment-lined baking sheet and freeze until firm, then transfer to a freezer-safe container or bag. Freeze for up to 2 months. Thaw overnight in the refrigerator or at room temperature for 1–2 hours. For a just-baked feel, warm briefly in a 300°F (150°C) oven for 5–10 minutes.

Nutrition (per serving)

Approximate values per bar (1 of 16): about 300 calories, 15 g fat, 45 g carbohydrates, 2 g fiber, 4 g protein, and 23 g sugar. These numbers are estimates and will vary based on the exact ingredients and bar size.