Step 1

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.⁣

Step 2

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.

Step 3

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.⁣

Step 4

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.⁣

Step 5

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.)⁣

Step 6

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.⁣

Step 7

Store the bars covered in the refrigerator for up to four days or allow to cool and freeze for up to three months.⁣