Blueberry Oat Crumble Bars are irresistible and surprisingly simple to make. A buttery oat crumble serves as both the base and the topping, producing a tender, golden crust and a crunchy finish. The filling uses fresh blueberries and a few pantry staples—no pre-cooking required—so you can assemble and bake these bars quickly. A bright blueberry glaze made from powdered freeze-dried blueberries and jam adds a vibrant finish and extra flavor.
Why you’ll love these Blueberry Bars:
- Easy one-bowl prep – The same oat mixture is used for both crust and topping, saving time and dishes. The blueberry filling is mixed raw, so there’s no extra cooking step.
- Handheld dessert – These bars combine the best of a blueberry pie and an oat crisp into a portable, shareable treat.
- Perfect for gatherings – They travel well and are great for potlucks, cookouts, or casual dessert tables.
Ingredient Overview:
The full recipe with exact measurements and the printable recipe card appears near the bottom of this page. Use this overview to understand key ingredients and substitutes.
- Butter – Salted butter gives the best flavor; use unsalted if you prefer but add a pinch of salt.
- Rolled oats – Use old-fashioned rolled oats for texture; quick oats will make a softer, less substantial crumble.
- All-purpose flour – For accurate results, spoon and level the flour into the measuring cup or weigh it on a kitchen scale.
- Fresh blueberries – For the best flavor, use berries in season (typically June through August). Frozen can work in a pinch but may change the texture.
- Cornstarch – Essential for thickening the blueberry juices so the filling sets while baking. Don’t skip it.
Substitutions & Variations
Gluten-free: You can try a cup-for-cup gluten-free flour blend and certified gluten-free oats; results may vary.
Dairy-free: Use a dairy-free butter or a solid plant-based baking stick.
Other fruits: This recipe is calibrated for blueberries. If you want other fruit fillings, consider recipes developed for those fruits (strawberries, peaches, apples, or cherries) since moisture and sweetness differ.
How to Make Blueberry Crumble Bars:
Step 1 — Prep the blueberries: In a medium bowl, combine fresh blueberries with granulated sugar, corn starch, cinnamon, vanilla, and lemon juice. Stir gently until evenly coated and set aside while you prepare the base.
Step 2 — Make the base and crumble topping: Melt the butter in a medium bowl, then stir in the flour, brown sugar, rolled oats, cinnamon, baking soda, and salt until combined. Reserve about 2 cups of this mixture to use as the crumble topping.
Step 3 — Pre-bake the crust: Press the remaining oat mixture evenly into a parchment-lined 9×13-inch pan. Bake at 350°F (175°C) for about 8 minutes until it firms slightly and begins to color. Remove from the oven.
Step 4 — Assemble and finish baking: Spread the blueberry mixture evenly over the warm pre-baked crust, then sprinkle the reserved crumble evenly over the berries. Return the pan to the oven and bake at 350°F for 36–44 minutes, or until the crumble is deep golden and the filling is bubbling and thickened. An instant-read thermometer placed in the filling should read about 190–200°F when done. Let the pan cool on a rack for about 30 minutes before glazing.
Step 5 — Make the glaze: In a small bowl, whisk powdered sugar with powdered freeze-dried blueberries, blueberry jam, vanilla, and enough water to reach a smooth, drizzle-able consistency. Taste and adjust sweetness or thickness as needed. Drizzle the glaze across the bars after they have cooled 30–60 minutes so the glaze sets without melting away.
Serving & Storing:
Allow the bars to cool for at least 1–2 hours before slicing so the filling sets. Store cooled bars in an airtight container in the refrigerator for up to 4–5 days. For longer storage, freeze unglazed bars wrapped tightly in plastic and foil; thaw in the refrigerator overnight or at room temperature for a few hours. If freezing individual portions, wrap pairs in parchment and foil for convenience.
Expert Baking Tips
Oven accuracy: An oven thermometer helps you confirm that your oven runs at the correct temperature—an important step for reliable baking results.
Weigh ingredients: Whenever possible, use a kitchen scale for flour and oats to ensure consistent results. Volume measurements vary depending on technique and measuring tools.
Other Blueberry Favorites
Crisps & Cobblers
Best One-Bowl Blueberry Crisp
Cheesecake
Double Blueberry Cheesecake
Desserts & Baking
Blueberry Cinnamon Rolls
Cake & Cupcakes
Blueberry Coffee Cake
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Blueberry Oat Crumble Bars
Ingredients
For the Base & Topping:
- 1 1/2 cups salted butter, melted (340 g)
- 3 cups all-purpose flour, spooned & leveled (390 g)
- 3 cups old-fashioned rolled oats (195 g)
- 1 1/2 cups light brown sugar, packed (330 g)
- 1 1/2 tsp baking soda
- 1/2 tsp salt
- 1/4 tsp cinnamon
For the Blueberries:
- 5 cups fresh blueberries (about 777 g)
- 1/3 cup + 1 tbsp granulated sugar (83 g)
- 4 tsp corn starch (12 g)
- 1/4 tsp cinnamon
- 1 tbsp lemon juice (15 g)
- 1 tsp vanilla extract
For the Glaze:
- 1 cup powdered sugar (115 g)
- 3 tbsp freeze-dried blueberries, pulsed to a powder
- 2 tbsp blueberry jam (40 g)
- Water, as needed to thin
- 1 tsp vanilla extract
Instructions
- Preheat: Preheat oven to 350°F. Spray a 9×13-inch pan with nonstick spray and line with parchment paper.
- Prep the filling: Rinse and pat dry the blueberries. In a medium bowl, combine blueberries, granulated sugar, corn starch, cinnamon, lemon juice, and vanilla. Stir gently and set aside.
- Make the base: In a medium bowl, melt the butter and stir in flour, oats, brown sugar, baking soda, salt, and cinnamon. Reserve 2 cups (324 g) of this mixture for the topping and press the remainder evenly into the prepared pan.
- Pre-bake the crust: Bake the crust for 8 minutes at 350°F, then remove from the oven.
- Assemble: Spread the blueberry mixture over the warm crust, then sprinkle the reserved crumble evenly over the berries.
- Bake: Bake at 350°F for 36–44 minutes, until the topping is a deep golden brown and the filling is thick and bubbling. The filling should reach about 190–200°F on an instant-read thermometer. Cool on a rack for about 30 minutes.
- Glaze: Whisk powdered sugar, freeze-dried blueberry powder, blueberry jam, vanilla, and enough water to make a drizzle-able glaze. Adjust thickness, then drizzle over the bars after they have cooled 30–60 minutes.
- Serve & store: Allow bars to cool for 1–2 hours before slicing. Store in an airtight container in the refrigerator for up to 4–5 days. Freeze unglazed bars for longer storage.
Nutrition
Nutrition information is estimated and should be used as an approximation.