For Topping: Whisk first 4 ingredients in bowl to blend. Add butter and rub in with fingertips, pressing until moist clumps form Mix in nuts. (Topping can be made 1 day ahead. Cover and chill.)
for Filling: Preheat oven to 375. Place blueberries in 13x9x2-inch glass baking dish or 3-quart round baking dish with 2-inch-high sides. Add sugar, lemon juice, cornstarch and cinnamon to berries; toss gently to blend. Spread berry mixture evenly in dish; sprinkle topping over. Bake until topping is brown and filling is bubbling thickly, about 50 minutes.
Bake
2000, 2001, 2003, 2017