Make the filling: 1. In a large bowl, mix together sugar, cornstarch and salt. Add blueberries, lemon juice and lemon zests and toss to coat. Set aside. Make the topping and assemble: 2. Preheat oven to 375°F. 3. In a large mixing bowl, stir together flour, coarse-grind cornmeal, sugar and salt. Using your hands, work in butter until mixture is crumbly and holds together when squeezed. Add corn and toss to evenly distribute. Press topping between your fingers and break into large pieces over filling. 4. Add blueberry mixture into a 2-qt. baking dish and sprinkle with the cornmeal crumble. 5. Bake until topping is golden and blueberries are bubbling, thick, and syrupy, 45 minutes. 6. Transfer to a wire rack and let cool 30 minutes, to allow the natural pectin to set, before serving.