Preheat the oven to 350°F and lightly grease a 1 ½ - 2 quart baking dish.
Combine the blueberries, sugar, cornstarch, lemon juice, and cinnamon. Transfer to the prepared dish.
18 ounces fresh blueberries, ½ cup granulated sugar, 3 tablespoons cornstarch, 1 tablespoon freshly squeezed lemon juice, ½ teaspoon ground cinnamon
To Make the Topping:
Combine all the topping ingredients in a medium bowl using a pastry cutter or your hands. The butter should be fully mixed in without any dry, sandy patches.
⅔ cup old-fashioned rolled oats, 6 tablespoons unsalted butter, ¼ cup all-purpose flour, ½ cup light brown sugar, 3 tablespoons granulated sugar, ⅛ teaspoon salt, ¼ teaspoon ground cinnamon
Sprinkle the crumble topping evenly on the filling.
Bake for 30-35 minutes until the filling is bubbly and the topping is golden brown and crunchy.
Serve warm with a scoop of vanilla ice cream.
Notes
*The calories listed are an approximation based on the ingredients in the recipe card and a serving size of 1 cup of crisp. Actual calories will vary.*Taste the blueberries before you start. If they’re tart, consider adding more sugar.