Blueberry Crumble Bars

These Blueberry Crumble Bars are the perfect balance of buttery, crumbly, and fruity. They feature a crisp oat crumble base, a juicy blueberry filling bursting with fresh flavour, and a golden crumble topping that bakes to perfection.

Whether you're looking for an easy summer dessert, a sweet afternoon treat, or something special to enjoy with a cup of coffee, these bars are simple to make using everyday ingredients. They can be served warm with ice cream or chilled for a delicious grab-and-go snack.

Servings: 9 bars - Prep: 20 min - Cook: 38 minutes - Total: 58 minutes

Ingredients

Crumble Base & Topping

160 g plain flour (1⅓ cups all-purpose flour)
80 g rolled oats (about 1 cup)
90 g light brown sugar (about ½ cup, packed)
½ tsp baking powder
Pinch of salt
120 g cold unsalted butter, cubed (8½ tbsp)
1 tsp vanilla extract

Blueberry Filling

300 g blueberries, fresh or frozen (about 2 cups)
45 g caster sugar (3½ tbsp)
1 tbsp lemon juice
Zest of ½ lemon (optional)
1 tbsp cornflour (cornstarch)
1 tsp vanilla extract

Instructions

1. Prepare the Tin

Preheat the oven to 180°C (160°C fan) / 350°F. Line a 20 cm (8-inch) square baking tin with baking paper, leaving an overhang on two sides so the bars can be lifted out easily after baking.

2. Make the Crumble Mixture

In a large mixing bowl, combine the flour, rolled oats, brown sugar, baking powder, and a pinch of salt. Add the cold cubed butter and vanilla extract.

Rub the butter into the dry ingredients using your fingertips until the mixture resembles coarse breadcrumbs. It's perfectly fine to leave a few larger buttery crumbs, as they create a lovely crunchy topping.

3. Press the Base

Transfer about two-thirds of the crumble mixture into the prepared baking tin. Press it down firmly into an even layer using the bottom of a glass or measuring cup. Reserve the remaining crumble mixture for the topping.

4. Pre-Bake the Base

Bake the base for 12–15 minutes, or until it looks lightly set and just begins to turn golden around the edges.

5. Make the Blueberry Filling

While the base bakes, place the blueberries, caster sugar, lemon juice, lemon zest (if using), cornflour, and vanilla extract into a bowl. Mix gently until the blueberries are evenly coated.

6. Add the Filling

Spread the blueberry mixture evenly over the warm baked base. Avoid pressing the berries down too firmly.

7. Add the Crumble Topping

Sprinkle the remaining crumble mixture evenly over the blueberries. Leave a few patches of blueberries visible so the finished bars have a beautiful burst of colour.

8. Bake

Return the tin to the oven and bake for 20–25 minutes, or until the crumble is golden brown and the blueberry filling is bubbling around the edges.

If the topping begins to brown too quickly, loosely cover the tin with foil during the last 5 minutes of baking.

9. Cool Completely

Allow the crumble bars to cool in the tin for at least 1 hour. For neat, clean slices, chill them in the refrigerator for 30–60 minutes before cutting.

10. Slice and Serve

Lift the bars out using the baking paper. Cut into 9 squares and serve as they are, dusted with icing sugar, or with a scoop of vanilla ice cream or a spoonful of Greek yoghurt.

Tips and Tricks

✅ Use cold butter straight from the fridge for the best crumbly texture.

✅ Don't overwork the crumble mixture. A few larger buttery crumbs create a crisp, crunchy topping.

✅ Fresh and frozen blueberries both work well. If using frozen blueberries, use them straight from the freezer without thawing first.

✅ When using frozen blueberries, increase the cornflour to 1½ tablespoons to help absorb the extra juice they release.

✅ Press the base down firmly so it holds together well after baking.

✅ Let the bars cool completely before slicing. Chilling them for 30–60 minutes makes it much easier to achieve clean, neat squares.

✅ Add a little lemon zest to brighten the blueberry flavour without making the filling overly sweet.

✅ Serve warm with vanilla ice cream or enjoy chilled with a cup of tea or coffee.