makes 24 bars
2 cups rolled oats
1 1/2 cups (plus up to 2 tablespoons more if necessary) unbleached all-purpose flour
1 cup light brown sugar
1/2 teaspoon fine sea salt
12 tablespoons (1 1/2 sticks) unsalted butter, melted
4 cups blueberries (fresh or frozen), divided
2 teaspoons cornstarch
2 tablespoons lemon juice
2 tablespoons granulated sugar, divided
1. Preheat the oven to 375 degrees. Line a 9x13-inch baking dish with parchment paper, leaving an overhang on two sides. Set aside.
2. In a large bowl, whisk together the oats, flour, brown sugar, and salt. Stir in the melted butter until small clumps form. If the crumb mixture seems too damp, stir in an additional two tablespoons of flour. Reserve 1 cup of the crumb mixture. Press the remaining crumb mixture into the bottom of the prepped baking dish.
3. Spread two cups of blueberries over top the crust. Sprinkle with cornstarch, lemon juice, and 1 tablespoon sugar. Then add the remaining blueberries and top with the remaining 1 tablespoon of sugar. Sprinkle evenly with the reserved crumb topping.
4. Bake in the oven for 30-40 minutes, or until the topping is golden brown and fruit is bubbling. Remove from the oven and let cool. Chill in the fridge for slightly crisper bars. Cut into squares with a sharp knife. Store any leftovers in a covered container in the refrigerator.