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There is something especially lovely about a bake that works equally well beside an afternoon cup of tea and warmed for pudding after dinner. These blueberry crumble bars have a buttery oat base, a generous layer of glossy blueberries and a softly crisp crumble topping. They look rather special once sliced, yet the preparation is genuinely uncomplicated.
The crumble mixture does double duty as both the base and the topping, which keeps the washing-up sensible and gives every layer the same warm vanilla flavour. A tin of blueberry pie filling makes this an exceptionally quick bake, while the easy homemade alternative uses fresh or frozen blueberries when the imported filling is difficult to find. Either way, the fruit stays bright and jammy against the golden oats.
Serve the bars cool when you want neat slices for lunchboxes, picnics or a cake stand. If the occasion calls for something more indulgent, warm one gently and add a scoop of good vanilla ice cream. That small contrast between hot berries, buttery crumble and melting ice cream turns a straightforward traybake into a gorgeous little dessert.
Why You’ll Love These Blueberry Crumble Bars
- They are wonderfully easy. One crumble mixture creates both the base and topping, so there is no separate pastry to roll or chill.
- You can use a shortcut or make the filling. Tinned blueberry filling is quickest, while the homemade option works beautifully with supermarket blueberries.
- They suit more than one occasion. Cut small squares for an afternoon treat or serve larger bars warm with ice cream for pudding.
- The textures are excellent. The firm oat base, soft fruit and crumbly golden top make every bite feel properly satisfying.
- They can be made ahead. The bars keep well for several days and slice most neatly once completely cool.
- The recipe is easy to vary. Raspberries, blackberries, cherries or mixed summer berries can all replace the blueberries.
What You’ll Need for Blueberry Crumble Bars
The quickest version uses only four main ingredients. If blueberry pie filling is unavailable, make the simple fruit layer below before preparing the crumble.
For the oat crumble
- 425g vanilla sponge cake mix
- 225g quick-cook porridge oats
- 170g unsalted butter, melted and slightly cooled
- ½ tsp fine sea salt
For the blueberry layer
- 600g blueberry pie filling
Or make your own with:
- 500g fresh or frozen blueberries
- 90g caster sugar
- 25g cornflour
- 1 tbsp lemon juice
- 1 tsp finely grated lemon zest, optional
Note: Vanilla or yellow cake mix is usually stocked in the home-baking aisle, with Betty Crocker being the easiest brand to find. Blueberry pie filling is less common. Use the homemade filling above, or substitute a thick blueberry compote and reduce it in a saucepan until it no longer runs from a spoon. Standard rolled oats also work, but quick-cook oats give a more cohesive crumble.
Equipment You’ll Need
- Digital kitchen scales
- A large mixing bowl
- A 23 x 33cm baking tin
- Baking paper
- A flexible spatula
- A medium saucepan, only if making the blueberry filling
- A sharp knife for cutting the cooled bars
No mixer is needed. A light-coloured metal tin gives the most even golden base, but a glass or ceramic dish will work if that is what you have.
How to Make Blueberry Crumble Bars
Step 1: Make the blueberry filling if needed
Place the blueberries, sugar, cornflour, lemon juice and zest in a saucepan. Cook over a medium heat for 6 to 8 minutes, stirring gently, until the berries release their juices and the mixture becomes glossy and thick. Set it aside to cool while you prepare the tin. The filling should mound softly on a spoon rather than pour like sauce.
Step 2: Prepare the tin and oven
Heat the oven to 170°C fan, 190°C conventional or 375°F. Lightly grease a 23 x 33cm tin and line it with baking paper, leaving an overhang on two sides. The paper makes it much easier to lift out the cooled bake without disturbing the crumble.
Step 3: Mix the oat crumble
Combine the vanilla cake mix, oats and salt in a large bowl. Pour in the melted butter and stir until no dry patches remain. The mixture should form soft clumps when pressed between your fingers rather than looking like a smooth dough.
Step 4: Press in the base
Set aside approximately one third of the crumble mixture for the topping. Tip the rest into the lined tin and press it into a firm, even layer using the base of a glass or your fingertips. Pay particular attention to the corners so the finished bars have an even base and do not crumble when lifted.
Step 5: Add the blueberry filling
Spoon the cooled blueberry filling over the base and spread it gently to the edges. Avoid scraping the paper or pressing too firmly, which can pull crumbs into the fruit. Leave a very slim border around the edge if your filling is particularly loose.
Step 6: Add the crumble topping
Scatter the reserved mixture evenly over the blueberries, keeping some pieces in generous clusters. Press it down only very lightly so the topping stays textured. A few visible pockets of blueberry are lovely and help the bars look homemade rather than overly perfect.
Step 7: Bake until golden
Bake for 22 to 28 minutes, until the top is lightly golden and the blueberry filling is bubbling at the edges. Leave the bake to cool completely in the tin before lifting it out with the paper. For the neatest squares, refrigerate it for 30 minutes after cooling and wipe the knife between cuts.
Tips for the Best Blueberry Crumble Bars
Thicken homemade filling properly. A runny fruit layer will soak into the base and make the bars difficult to lift, so cook it until glossy and spoonable.
Use quick-cook oats for neat slices. Their smaller flakes bind more closely with the cake mixture and melted butter.
Press the base firmly. The topping should be loose and craggy, but the bottom layer needs enough pressure to become a stable crust.
Cool before cutting. Warm bars taste gorgeous but will not hold a tidy shape. Allow the fruit to set before slicing if appearance matters.
Keep some large crumble clusters. Breaking every piece into fine crumbs removes the lovely contrast on top.
Add one polished touch. A little lemon zest in the berries or a dusting of icing sugar just before serving lifts the flavour and makes the tray look beautifully finished.
Scale with the right tin. For a half batch, use a 20cm square tin rather than spreading the mixture too thinly in a large tray.
Make It Your Own
Raspberries and blueberries make a particularly lovely combination. Use equal quantities and add another teaspoon of cornflour because raspberries release plenty of juice as they cook.
For apple and blueberry crumble bars, replace half the berries with finely diced peeled apple and simmer the filling for a few extra minutes. A pinch of cinnamon works beautifully with this version.
White chocolate brings a sweeter, more indulgent finish. Scatter 75g chopped white chocolate over the fruit before adding the crumble, or drizzle a little melted chocolate over the completely cooled bars.
For extra crunch, replace 50g of the oats with chopped almonds or pecans. Toasted flaked almonds can also be scattered over the top for the final 5 minutes of baking.
If you would rather avoid a cake mix, use 250g plain flour, 180g light brown sugar, 225g oats, 1 teaspoon baking powder, 1 teaspoon vanilla and 250g melted butter. The from-scratch version is slightly more crumbly but has the same easy layered method.
Frequently Asked Questions
Yes. Frozen blueberries work very well in the homemade filling and do not need to be defrosted first. Cook them until the juices thicken fully, allowing an extra minute or two if necessary.
Make a quick filling with 500g blueberries, 90g caster sugar, 25g cornflour and 1 tablespoon lemon juice. Simmer it until thick and glossy, then cool it before assembling the bars.
The fruit filling was probably too loose or the bars were cut before cooling. Cook homemade filling until it mounds on a spoon, bake until the edges bubble and let the tray cool completely before slicing.
Yes. Bake them up to two days ahead and keep them covered in a cool place or in the fridge. Bring chilled bars to room temperature before serving, or warm individual portions for pudding.
Yes. Freeze completely cooled bars in a single layer before transferring them to an airtight container with baking paper between layers. Keep them frozen for up to three months and defrost at room temperature.
They can stay in a cool room for one day, but refrigeration is best for longer storage, particularly when using homemade fruit filling. Keep them covered for up to four days so the bars do not absorb fridge odours.
How to Store Blueberry Crumble Bars
At room temperature: Keep cooled bars in an airtight container for up to one day if the room is cool. Place baking paper between layers to protect the crumble.
In the fridge: Refrigerate them in an airtight glass storage container for up to four days. Let them sit at room temperature for 20 minutes before serving, or warm individual bars gently.
In the freezer: Freeze the bars for up to three months with baking paper between layers. Defrost them at room temperature, then place them in a 160°C fan or 180°C conventional oven for 5 minutes if you would like to refresh the topping.
Blueberry Crumble Bars Recipe Card
Recipe name: Easy Blueberry Crumble Bars with a Golden Buttery Topping
Description: Buttery oat crumble bars layered with glossy blueberries, equally lovely served cool with tea or warm with vanilla ice cream.
Prep time: 20 minutes
Cook time: 25 minutes
Cooling time: 1 hour
Total time: 1 hour 45 minutes
Servings: 18 bars
Estimated cost: Approximately £9 per batch or £0.50 per bar
Calories: Approximately 280 calories per bar when made with tinned filling. Nutritional figures are estimates only.
Equipment
- Digital kitchen scales
- Large mixing bowl
- 23 x 33cm baking tin
- Baking paper
- Flexible spatula
- Medium saucepan if making the filling
- Sharp knife
Ingredients
- 425g vanilla sponge cake mix
- 225g quick-cook porridge oats
- 170g unsalted butter, melted
- ½ tsp fine sea salt
- 600g blueberry pie filling, or homemade filling using 500g blueberries, 90g caster sugar, 25g cornflour, 1 tbsp lemon juice and 1 tsp lemon zest
Instructions
- If needed, simmer the homemade filling ingredients for 6 to 8 minutes until thick and glossy, then cool.
- Heat the oven to 170°C fan, 190°C conventional or 375°F. Grease and line a 23 x 33cm tin.
- Mix the cake mix, oats and salt, then stir in the melted butter until crumbly.
- Reserve one third of the crumble and press the remainder firmly into the tin.
- Spread over the blueberry filling and scatter with the reserved crumble.
- Bake for 22 to 28 minutes until lightly golden and bubbling at the edges.
- Cool completely before lifting out and cutting into 18 bars.
Notes
- Quick-cook oats produce the neatest slices.
- Cool the bars fully before cutting.
- Use frozen blueberries straight from the freezer when making the filling.
- Freeze finished bars for up to three months.
More Easy Bakes
If you make these blueberry crumble bars, leave a comment or share them with me on Instagram. Try my strawberry cream cheese bars next, or browse the full recipe index for more baking inspiration.
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