Whisk together the white granulated sugar and cornstarch in a large bowl. Sprinkle over blueberries and toss so that they are all covered with mixture. Place blueberries in the bottom of a 9 x 9 baking dish. Combine the flour, oats, brown sugar, ground cinnamon and chopped nuts in a large bowl. Melt the butter in the microwave or on the stove and pour into the flour mixture. Mix until it is all wet. Spread or sprinkle the oat topping over the blueberries and bake in preheated 375 degree oven for 35 to 40 minutes until bubbling and browned on top. Makes 6 to 8 servings. Enjoy!