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Blueberry Oatmeal Bars

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4.77 from 21 votes

These blueberry oatmeal bars are just the right amount of sweet with their juicy blueberry filling, soft and buttery oatmeal crust, and golden crumb topping! Keep the blueberry train rolling with my blueberry muffin bread or blueberry smoothie bowl.

Blueberry Oatmeal Bars stacked on a plate

Deep thought on this Sunday: What if they had called blueberries “purpleberries”?

Every time I mash or cook a blueberry and I see the purple inside, that’s what I think. It’s almost like I resent them for being called blueberries.

Because it’s almost like false advertising. Sure, they’re blue on the outside, but aren’t we taught that it’s what’s on the inside that counts?

What if this recipe were actually called Purpleberry Oatmeal Bars? It sounds like something straight out of Willy Wonka. But I guess we have plenty of oddly named fruits: dragon fruit, kumquats, boysenberries.

And breadfruit – IT’S NOT BREAD, PEOPLE. FFS.

Close up of purple blueberry oatmeal bars

I should really put in charge of naming things, I’m really good at it. Examples:

  • Dragon fruit = Pink Poppy Seed Alien Football 
  • Kumquat = Oblong Oranges
  • Boysenberries = Almost Raspberries
  • Breadfruit = Goosebump Limes

Impressed? Thought so.

A yellow pan full of blueberry oatmeal bars

What if it’s not blueberry season?

Depending on where you live, you might be looking at this recipe thinking to yourself, “Leslie, it is not yet the appropriate time for me to go blueberry picking and now you have made me sad”.

Fear not! I usually make these with frozen blueberries and they are equally as delicious. So just grab a bag out of your store’s frozen section and you’re all set.

Blueberry Oatmeal Bars on a cooling rack

If you can make this recipe as is, fabulous! Easy peasy. But if you have dietary restrictions, or maybe your pantry is just lacking in the right ingredients, there are some substitutes you can make without it getting complicated.

Ingredient substitutions

Overhead shot of sliced blueberry oatmeal bars on parchment paper

These blueberry oatmeal bars have taken me quite a while to get right – I’m always surprised at how much even a 1/2 teaspoon of an ingredient can throw off the whole thing.

I wanted the base to be chewy, buttery and sturdy enough to hold the filling. One time I used too much butter and it spread too much and never cooked through.

Another time I tried a 1:1 ratio of oatmeal and flour, and the crust was too thick and seemed dry.

I had tried to avoid adding sugar, but it needed it for the right flavor. And the 1/2 teaspoon of pure vanilla extract is what really brought it all together for me. 

I had also tried making the crust and crumb topping as two separate things, with two different sets of ingredients. It was entirely too complicated, and didn’t need to be. Using the same thing for both works out perfectly.

Sliced blueberry oatmeal bars on parchment paper

I also wanted the filling to be freshly made and not some canned pie filling – but I struggled with getting the right mix of ingredients for a long time. An embarrassingly long time.

Additionally, I knew I wanted lemon juice and zest in there, because blueberries + lemon = <3. But the amount of liquid that the lemon juice added really screwed me up. Blueberries get super juicy when they cook, and I just couldn’t get the ratios right.

The key to my eventual success was the right amount of cornstarch. Too much and it was weirdly gelatinous. Too little, and the filling was too wet and the bars just fell apart. One teaspoon was just right. 

Blueberry Oatmeal Bars stacked on a plate

Can I make them in a 9″x13″ pan?

I haven’t tried to make these in a 9 x 13 dish, but I would imagine if you doubled the recipe you’ll just end up with slightly thicker bars as a result. 

This recipe (made in an 8″x8″ pan) can yield 9 large bars, or 16 smaller bars. Another way of saying that is, “You can cut these into 16 bars, or 9 if you want to be able say you only ate one and get more bang for your buck.”

Blueberry Oatmeal Bars stacked on a plate

I also have not tried making these with a mix of berries, but I’m aiming to soon. I’m thinking blueberries and blackberries, with a little extra lemon zest.

Or maybe I’ll make a 9 x 13 dish that’s half and half. Or maybe I’ll just double all the things, still bake it in an 8 x 8 dish, and make monstrously sized blueberry oatmeal bars that may or may not be a huge mistake.

I’ll report back later.

Blueberry Oatmeal Bars stacked on a plate

Get your blueberry on:

After you’ve made this recipe, please consider coming back to share your experience with others by leaving a comment below with a star rating!

Blueberry Oatmeal Bars stacked on a plate

Blueberry Oatmeal Bars

4.77 from 21 votes
These blueberry oatmeal bars are just the right amount of sweet with their juicy blueberry filling, soft and buttery oatmeal crust, and golden crumb topping!
Prep Time 5 minutes
Cook Time 38 minutes
Total Time 45 minutes
Servings 9 to 16 bars (depending on size)


  • 1 cup old-fashioned rolled oats, can substitute gluten free oats
  • ¾ cup all purpose flour, can substitute 1:1 gluten free flour
  • ¼ cup light brown sugar
  • ¼ teaspoon kosher salt
  • 6 tablespoons unsalted butter, melted (can substitute coconut oil, melted)
  • ½ teaspoon pure vanilla extract
  • ¼ cup granulated sugar
  • 1 tablespoon freshly squeezed lemon juice, about half a lemon
  • Zest of one lemon
  • 1 teaspoon cornstarch
  • 12 ounces fresh or frozen blueberries*


  • Preheat oven to 375° and line an 8×8 baking dish with parchment paper and coat with nonstick spray. Set aside.
  • In a large bowl, combine oats, flour, brown sugar and salt. Add melted butter and vanilla extract, and stir until flour is completely combined and mixture is lumpy.
  • Set aside a little less than 1/2 of the mixture in a small bowl, and press the rest into the bottom of your prepared pan. Set aside.
  • In a medium bowl, combine granulated sugar, lemon juice, lemon zest, and cornstarch. Add blueberries and carefully stir and/or toss the mixture to coat the blueberries.
  • Pour blueberry mixture evenly over crust in prepared baking dish.
  • Top with reserved oatmeal mixture - you'll still have some of the fruit showing through, and that's just fine!
  • Bake for 38-42 minutes or until the top is golden brown. Place on a wire rack to cool completely (or place in the fridge to cool it more quickly).
  • Use the edges of the parchment paper to lift the bars out of the pan, slice, and serve. Enjoy!



  • Store in the fridge, covered for up to 3 days. They'll become softer as time goes on, so eating them within the first day is recommended.
  • Reheat by microwaving for 10-15 seconds.
  • If gluten free, use gluten free oats and gluten free flour.
  • If dairy free or vegan, substitute melted butter for melted coconut oil.
  • *If using frozen blueberries, thaw, rinse and drain before using.


Calories: 207kcal | Carbohydrates: 32g | Protein: 3g | Fat: 8g | Saturated Fat: 5g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 2g | Trans Fat: 1g | Cholesterol: 20mg | Sodium: 69mg | Potassium: 86mg | Fiber: 2g | Sugar: 15g | Vitamin A: 254IU | Vitamin C: 5mg | Calcium: 17mg | Iron: 1mg
Course Dessert
Cuisine American
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