Rhubarb Crumble Bars
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If you adore baking with rhubarb like I do, these rhubarb crumble bars are going to become your new favourite bake. With a buttery oat crumble, a sweet and tangy rhubarb filling, and the perfect golden top these bars are easy to make and are absolutely delicious.
Notes from The Patisserie
These bars are perfect for spring and summer, especially during peak rhubarb season for the best flavour. The texture balance is great with the firmer and crunchy crumble and the soft jam like filling, whilst also just being packed full of flavour.
These are ideal for a bit of baking on them weekend, for afternoon tea, for a picnic, or for something simple to make to have with a cup of tea. They are great whether they are warm or cold, and they are freezer friendly.
These Rhubarb Crumble Bars are such a simple but comforting bake, and they are perfect if you adore classic crumble desserts. The combination of buttery oats and sharp rhubarb is always a winner, and once you make them you’ll definitely want to bake them again and again.
Ingredient notes and tips
The crumble, is a mixture of really basic store cupboard ingredients so it should be easy to buy everything if you don’t already have it
- Oats – I use rolled oats as I like the texture of the larger oats – you can swap to porridge oats
- Flour – plain flour is best (all purpose) as you need less raising agent than is present in self raising flour
- Sugar – I use light brown soft sugar because I like the flavour it brings to the crumble, but you can swap it to caster sugar if you want the sugar to be the same for both parts of the recipe
- Baking powder – a touch of baking powder to get the best texture of crumble
- Butter – I use block unsalted butter – I do not use a baking spread or margarine as they are too soft
The rhubarb mixture is designed to use fresh rhubarb that is either freshly picked, or in season – making most of that delicious flavour
- Rhubarb – I use fresh rhubarb, so it’s naturally quite green. You can use forced rhubarb which I much more pink in colour. You can use tinned rhubarb, but I would drain it and pat it dry (it may take less time to cook in the pan)
- Sugar – an added sweetness of caster sugar to combat the tart quality of the rhubarb, but also help create a jam like texture
- Lemon – an added bit of lemon zest and juice for flavour and set – you can leave it out, and use one tablespoon of water instead
- Vanilla – this is optional, but I love it
- Cornflour – I MUCH prefer using cornflour for this, instead of plain flour. I find plain flour does not work as well
Making homemade crumble mixture
As the crumble mixture is so basic, it’s also easy to make. The rolled oats give the best texture to the bars, whilst the brown sugar adds a natural caramel flavour that balances well with the rhubarb in the filling.
I would recommend rubbing everything together with your hands (as mentioned in the full recipe and method below) because you want the oats to resemble oats still, and not blitz them down to a powder. I find it best to use COLD butter to make this easier, as warm butter becomes messy. You can use a food processor to star the crumble mix, but I would add the oats in after blending the other ingredients
The rhubarb filling
As rhubarb can be naturally quite tart on its own, it balances well with the dash of sugar, the lemon zest and vanilla that are added into the filling. It helps create the jam like texture, softening the flavour but also keeping the core of what rhubarb is.
The lemon zest and juice is an added zingy touch whilst also helping the rhubarb mixture thicken and set. It’s about flavour, and formula, whereas the cornflour is there to help make sure it stays together and doesn’t go sloppy once baked.
Make sure to let the bars cool fully as they could easily fall apart whilst still warm – as a normal crumble dessert world. I would also say it’s super important to use the correct tin size as changing it can make quite a difference to the bake time and end result.
FAQs
Yes, you can, but I would recommend thawing it first and draining any excess moisture to prevent it being too wet. It may need a little less/more cooking time in the pan
You can try using a gluten free plain flour blend and gluten free oats, although I haven’t personally tested it.
Yes, it should work with dairy free alternatives, but the oat mixture might be a little softer
Yes – you can find a raspberry version here, a lemon version here, or you can swap this to other berries such as strawberries
The crumble topping should be golden brown and the filling should be bubbling slightly around the edges.
Rhubarb Crumble Bar Recipe
Ingredients
Crumble
- 175 g rolled oats
- 200 g plain flour
- 150 g light brown soft sugar (or caster sugar)
- 1/2 tsp baking powder
- 175 g unsalted butter (cold and cubed)
Filling
- 500 g fresh rhubarb (trimmed/chopped)
- 50 g caster sugar
- Zest of 1 lemon
- 1 tbsp lemon juice
- 1 tbsp cornflour
Instructions
Crumble
- Preheat the oven to 200ºc/180ºfan and line a 9×9" square tin with parchment paper.
- In a large bowl, add the rolled oats, plain flour, light brown soft sugar, baking powder and unsalted butter.
- Rub the ingredients together with your fingers until the mixture resembles bread crumbs and there are no large lumps of butter left.
Filling
- In a pan, add the prepared rhubarb, caster sugar, lemon zest/juice, and vanilla extract. Heat gently on a low heat until the rhubarb starts to soften slightly.
- Add the cornflour and stir through for another 1-2 minutes until slightly thickened. Leave the filling to cool for 10 minutes.
Assembly
- Pour 500g of the oaty crumble mix into the lined tin and press down firmly.
- Spread the rhubarb filling evenly over the base, and then sprinkle over the remaining crumble mixture.
- Bake in the oven for 30 minutes or more, until golden, crisp, and beautiful.
- Leave the bars to cool fully before portioning. Refrigerating them can sometimes make this easier.
Notes
- These beauties will last for 3+ days, best in the fridge
- I use this tin for this bake
- These can freeze for 3+ months
Storage + Freezing
These Rhubarb Crumble Bars will last for 3-4 days at room temperature in an airtight container, or slightly longer in the fridge.
They also freeze really well. Simply wrap the sliced bars individually and freeze for up to 3 months. Or, you can freeze the whole traybake as well