These delicious blueberry rhubarb crumble bars are made with a layers of deliciously sweet crumble that sandwich the most vibrant and flavorsome tart blueberry rhubarb jam between them. Ready in less than 30 minutes, these crumble bars make a lovely afternoon treat or fruity dessert.

The sweet and tart blueberry rhubarb jam that features in this recipe is the real centerpiece of this delicious recipe. With zesty lemon juice running through it, I could literally eat it by the spoonful! Not a fan of bluberry rhubarb goodness? I could never, but these delicious raspberry rhubarb bars are an equally good alternative.

However, the sweetness of the blueberries and the tartness of the rhubarb (picked fresh from my allotment in the summer months!) is complemented even more by a buttery, shortbread base and sugary-sweet crumble topping.

Ingredient Notes & Equipment For Making Blueberry Rhubarb Crumble Bars

Scroll down to the recipe card for the exact quantities you’ll need for this recipe, plus step-by-step instructions. I’ve added a few notes on each ingredient, plus the equipment you’ll need.

Equipment

To bring these blueberry rhubarb bars into fruition (hehe, pun intended!), you’ll need a saucepan for making the blueberry rhubarb jam and a wooden spoon for stirring. Then, you’ll need a baking dish for making your crumble bars.

I’d recommend a 7 x 7 baking tin lined with baking paper.

Ingredient notes

Here are the ingredients you’ll need plus some notes (exact quantities are in the recipe card).

• Rhubarb: You can either use fresh rhubarb or frozen rhubarb, both will work just fine!
• Blueberries: Again, frozen or fresh blueberries will work just fine in this recipe.
• Golden caster sugar: I find the texture and taste of golden caster sugar best-suited for this recipe, but you could use normal caster sugar or granulated sugar if needed.
• Lemon: The addition of a little lemon zest and juice helps cut through the tartness of the blueberry rhubarb jam perfectly here.
• Cornstarch: Cornstarch works as a much-needed thicker for the jam. You could also use tapioca starch or even chia seeds for a slightly different texture.
• Cinnamon
• Plain flour: We use standard plain flour for the crumble bar base and crumble topping. To make this recipe gluten-free, you could use gluten-free all-purpose flour.
• Oats: I find the addition of steel-cut oats adds a lovely texture and taste to these bars.
• Butter: If you are plant-based or dairy-free, you could use olive oil or coconut oil instead in this recipe.
• Brown sugar: Brown sugar is best for the crumble component of these bars. Use the same caster sugar as above if essential.
• Baking powder

Making Your Blueberry Rhubarb Crumble Bars

Step 1) Make Your Blueberry Rhubarb Jam

To make the jam, combine all the ingredients (chopped rhubarb, blueberries, sugar, lemon juice and zest, cornstarch, and cinnamon) in your saucepan. Put the saucepan over low heat on the hob and allow the jam to simmer for around 30 minutes until the fruit has cooked until thick and jammy.

Step 2) Make The Crumble

While the jam is simmering, you can start making the crumble component of this recipe. You should also begin to preheat your oven and line your baking tray at this point.

To make the crumble, first combine all of the dry ingredients (so plain flour, brown sugar, oats, baking powder, and salt). Then, add the (slightly softened) butter chopped into small cubes and use your fingers to combine the butter and create a crumble texture.

Step 3) Assemble the base

Press about two-thirds of your crumble mixture into your baking tin, ensuring you press it down evenly across the whole tin. Bake for about 10 minutes.

Step 4) Assemble the bars

Once you’ve baked the base, you can pour over your jam, and then sprinkle over the remaining third of your crumble. Bake your blueberry rhubarb crumble bars for 25-30 minutes until the crumble is golden.

Allow your bars to fully cool and then refrigerate for a couple of hours before you cut them into bars. Otherwise, you risk the crumble, well, crumbling!

Storing

These blueberry rhubarb crumble bars are best stored in the refrigerator – there is something so delicious about enjoying the tart jam and sweet crumble layers when cold and fresh from the fridge.

You could also leave them on the side to get to room temperature before eating, though.

FAQs

Can I use something other than rhubarb or blueberry for the filling?

Yes, absolutely! You could use just blueberries or just rhubarb (alhoug these wuld be very tart indeed!). You could also try my raspberry rhubarb bars, or make the same crumble mixture with raspberries, strawberries, or mixed berries for an equally delicious bake.