How to Make It
Preheat oven to 375°.
Coat an 8-inch square glass or ceramic baking dish with cooking spray. Sprinkle 2 teaspoons cornstarch evenly in dish.
Combine remaining 2 teaspoons cornstarch, 2 tablespoons brown sugar, vanilla, and blueberries in a large bowl; toss. Place in prepared baking dish.
Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 6 ingredients (through cinnamon) in the bowl of a food processor; pulse twice to combine. Add butter; pulse 5 times or until the mixture resembles coarse meal. Spoon topping evenly over blueberries, packing down lightly. Bake at 375° for 30 minutes or until filling is bubbly and topping is golden.