Blueberry Crumble Bars

There is nothing I love more than fruit-focused desserts…they are perfect for any time of the year and are guaranteed to be a crowd pleaser. Sometimes desserts involving chocolate or cream can feel too rich and heavy, but fruit desserts are beautifully balanced because of their lightly sweet, tart, and buttery flavors. 

This recipe will become your go-to once you realize how quick and easy it is to slap together. The best part is how little time and effort is spent making the bars look “perfect”, the crumble topping will look unique and beautiful every time you make it. Less time garnishing, more time eating! 

I enjoy these bars cold, right out of the refrigerator, and served with a hot mug of tea or coffee. Because of the old-fashioned oats and fruit content of the recipe, I often argue that these bars are good in the mornings as breakfast. What do you think? 

Blueberry crumble bars with streusel topping
Blueberry crumble bars with streusel topping

Before you get started

  • Gather your equipment and ingredients so that you have them ready to go when it’s time to start cooking! 
  • Take the egg out of the fridge at least 30 minutes prior to bake time so that it’s at room temperature when you need to use it. This ensures that your crumble mixture has the right consistency so that the blueberry bars bake with the perfect texture. 
  • If using frozen blueberries, do not take them out of the freezer! Leave them inside to prevent thawing and add them in right before baking. 

Suggested Equipment & Appliances

  • 9” x 13” x 3” baking pan
  • Stand mixer or electric hand mixer
  • 1 Large mixing bowl
  • 1 medium mixing bowl
  • Wire cooling rack 
  • 1 wooden or plastic spoon 

Recipe Yield and Cook Time

  • Recipe Yield: 18 Servings
  • Prep Time: 25 minutes
  • Cook Time: 50 minutes
  • Cool Time: 20 minutes
  • Total Time: 1 hour 35 minutes

Ingredients

For the Crumble Layers:

  • 1 cup (2 sticks) unsalted butter, cut into small cubes
  • 1 cup packed brown sugar (light or dark)
  • 1 cup granulated (white) sugar
  • 3 cups all-purpose flour
  • 2 cups old fashioned rolled oats
  • 1 teaspoon kosher salt
  • 1 teaspoon baking powder
  • 1 large egg, at room temperature
  • 1 teaspoon vanilla extract

For the Blueberry Filling:

  • 3 cups fresh or frozen blueberries
  • 2 tablespoons fresh squeezed lemon juice (1 lemon) 
  • ⅓ cup granulated (white) sugar
  • 3 tablespoons instant tapioca

Instructions

  1. Preheat the oven to 350 degrees Fahrenheit. Grease a 9” x 13” baking dish with butter or non-stick cooking spray. 
  2. Either in the bowl of a stand mixer or using an electric hand mixer and large bowl, cream together the cold butter, brown sugar, and granulated sugar. Once the butter and sugars are well mixed, add in the egg and vanilla extract and mix once more to blend together. 
  3. Stir into the mixing bowl the all-purpose flour, rolled oats, salt, and baking powder until everything is evenly combined. Set this aside for now. 
  4. In a medium mixing bowl, stir together the ingredients for the blueberry filling. This includes either fresh or frozen (unthawed) blueberries, lemon juice, instant tapioca, and granulated sugar.
  5. Scoop about half of the prepared crumble mixture into the greased baking dish and press it into one even layer using your hands. Your goal in this step is to create a solid and sturdy crumble “crust”  to support the two layers that go on top. 
  6. Scoop the prepared blueberry filling into the dish and spread it into an even layer on top of the crumble crust. After this, sprinkle the remainder of the crumble mixture on top of the blueberry layer, making sure to cover all of the edges and corners. 
  7. Bake the blueberry crumble bars for 45-50 minutes or until the top layer of crumble is golden brown. 
  8. Once removed from the oven, let the dish cool on a wire rack for at least 20 minutes before cutting. If you try to slice up this gorgeous dessert while it’s still hot or warm, the bars won’t hold together or maintain their shape. 

Tips and Tricks

  • This recipe is best made with fresh blueberries, but if you only have frozen berries on hand, you can use them instead. Make sure not to thaw the frozen berries before mixing them up with the other ingredients! Follow the recipe as described with the berries cold and frozen. 
  • For optimal baking and perfect crumble bar texture, keep the oven door closed during the cooking time and center the baking pan on the middle rack. 
  • Instant tapioca, as listed in the recipe for the blueberry filling, is used as a thickening agent that is ideal for pie, cobbler, and crumbles! You can find instant tapioca in the baking aisle of your supermarket. See substitutions below for alternatives! 
  • If using bottled lemon juice instead of fresh squeezed, cut the quantity down to 1 tablespoon, as the bottled juices are more sour! 
  • These blueberry crumble bars will keep best for up to 1 week if stored in an airtight container and refrigerated! 
  • They will also keep well frozen for up to 3 months if stored in an airtight container. Before serving, let the crumble bars thaw overnight at room temperature. You can also speed up the defrosting process in the microwave if you’re short on time. 
  • If you really enjoy the tang and flavor infusion that the lemon juice adds to the blueberry filling, try adding in the zest of 1 lemon along with the other filling ingredients! 
  • If using salted butter instead of unsalted, use ½ teaspoon of salt in the crumble instead of 1 teaspoon as listed in the recipe. 

Substitutions

Any of the following ingredients can be swapped for some alternatives at the same quantity:

  • Instant Tapioca can be replaced with cornstarch, instant ClearJel, or arrowroot starch. 
  • Brown Sugar can be replaced with granulated (white) sugar, coconut palm sugar, or raw cane sugar! 

Blueberries Though they are the star of the show here, you can swap out the blueberries for your other favorite berries! Try strawberries, raspberries, or blackberries!