These homestyle crumb bars taste like blueberry crisp in bar form. The topping and crust is made from the same brown sugar-oat mixture. It’s sweet, crunchy and pairs perfectly with the blueberry filling.
To make things easy, you can use either fresh or frozen blueberries. If you’re using frozen berries, don’t let them thaw before making the filling. Simply use them from frozen and bake.
Let’s take a look at what you need to make a batch of these berry bars.
Oat Crust & Topping.
- Oats. Old-fashioned oats are my preference for these bars. They add a nice flavor and texture. Quick cook oats, which are flaky compared to old-fashioned, can be used. Blueberry bars made with quick cook oats are a smidgen more cake-like. But it that’s what you have on hand, don’t hesitate to use them. Don’t use steel cut oats. Those won’t work. If you’re gluten-free, use gluten-free oats.
- Flour. All-purpose or gluten-free flour helps the bars hold together.
- Sugar. Brown sugar adds a very subtle flavor to the crust. If you don’t have any in the house, use an equal amount of granulated sugar.
- Cinnamon. Ground cinnamon adds a nice flavor. You can also use pumpkin pie spice.
- Salt. Helps enhance all the flavors. Use table (fine) salt.
- Butter. A stick of cool butter is mixed into the oat-flour mixture. And cool is the key here. You want the butter to feel soft to the touch. This way it’s easy to mix into the other ingredients.
- Blueberries. Fresh and frozen blueberries work in this recipe. If you use fresh blueberries, remove any stems and wash the berries before using them. For frozen blueberries, don’t let them thaw before using them. Simply use the blueberries from frozen.
- Sugar. A little granulated sugar adds sweetness to the filling.
- Cornstarch. We need the filling to thicken and cornstarch is perfect for this. Since cornstarch needs to reach 212 to thicken, make sure the filling bubbles. That’s key.
- Lemon Zest and Juice. A little lemon zest and juice really help to bring out the flavor in the blueberry filling.
How to Make Blueberry Crumb Bars.
Step One: Make the Crust/Topping Mixture.
The crust and topping are made from the same easy-to-make streusel mixture. To make it, whisk together the oats, flour, brown sugar, cinnamon, and salt. If there are any clumps of brown sugar, break them up with your hands.
Add the soft butter. Do this with either your hands or a pastry cutter. When it’s mixed, you shouldn’t see any large pieces of butter left in the bowl. I like to test the mixture by giving it a squeeze. If it holds together easily, you’ve mixed it enough. If it falls apart or looks floury, keep mixing in the butter.
Remove about a cup of the mixture for the topping and set it aside. Press the remaining oat mix into a parchment-lined 8-inch square pan. It’s important to press the mixture firmly into the pan. This way, the crust won’t crumble apart when you cut the bars after they’re baked.
By the way, this streusel-like mix keeps great in the fridge. If you want, prepare it the night before you plan to bake. Just be sure to store it in a covered container to keep it from drying out.
Step Two: Prepare the Filling and Assemble the Bars.
The filling is so simple to put together. Start with washed and dried fresh blueberries or frozen blueberries. If they’re frozen, don’t let the berries thaw. They get too juicy and can make the bars soft.
Place the blueberries in a large bowl and add the sugar, cornstarch, lemon zest, and juice. Give this a good stir so that the blueberries are coated.
Spread the blueberries over the crust. Then sprinkle the reserved oat topping mixture all over the berries.
Step Three: Bake the Bars.
Place the pan into a preheated 350℉ oven. The bars take about 45 minutes to bake. Look for the topping to be light brown and the filling to bubble gently.
When they first come out of the oven, they’ll be very delicate. If you try to cut them right away, they can fall apart. Let the bars cool in the pan. Once they’re cool, lift the parchment or foil overhang and remove the bars from the pan. Place the bars on a cutting board and cut into squares.
Storage and Freezer Instructions.
Store your blueberry crumb bars in an airtight container in the refrigerator for up to 4 days. If you’d like to freeze them, let the bars cool. Then place in a freezer-safe container for up to 3 months. When you’re ready to eat, let them thaw in the refrigerator.
Blueberry Crumb Bars
For the Oat Crust and Topping
- 1 ½ cups old-fashioned rolled oats (4 ounces; 113 grams)
- 1 cup all-purpose flour (5 ounces; 142 grams)
- ½ cup brown sugar (3 ½ ounces; 100 grams)
- 1 teaspoon ground cinnamon
- ¼ teaspoon salt
- ½ cup butter, soft (4 ounces; 113 grams)
For the Blueberry Filling
- 2 cups blueberries (1 pint, see note)
- ¼ cup granulated sugar (1 ¾ ounces; 50 grams)
- 1 tablespoon cornstarch
- Finely grated zest of 1 medium lemon
- Juice of 1 lemon about 2 tablespoons
Preheat the oven to 350°F. Line an 8-inch square baking dish with parchment paper or aluminum foil, leaving a little overhang on all sides. (If you’re using parchment paper, you can clip it to the pan with binder clips. This holds it in place.) Grease the parchment or foil lightly with cooking spray; set aside.
Place the oats, flour, brown sugar, cinnamon, and salt in a large bowl. Stir to combine. Break up any piece of brown sugar with your hands or a fork.
Add the butter and, using a pastry cutter or your fingertips, incorporate until no large pieces of butter remain. The mixture should be crumbly and hold together when squeezed.
Set aside 1 cup of the mixture in a small bowl. Transfer the remaining mixture to the prepared baking dish and press it firmly and evenly into the pan to form the crust.
Place the blueberries in a medium bowl. Add the sugar, cornstarch, lemon zest and lemon juice and toss gently to combine. Spread the blueberries over the crust. Sprinkle the reserved crumb mixture over the blueberries. (Remove binder clips from pan now. They aren’t oven-safe.)
Bake until the filling is bubbling and the top is golden-brown, about 45 minutes. Let cool at least 2 hours before cutting into bars.
Store the bars covered in the refrigerator for up to four days or allow to cool and freeze for up to three months.
Use fresh or frozen blueberries. If you’re using frozen blueberries, don’t allow them to thaw being using.
For extra filling, increase the blueberries in the filling to three cups.