Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish (or an 8x8 inch dish for a thicker crumble).
Step 2: In a large bowl, gently combine the fresh blueberries, granulated sugar, lemon juice, lemon zest, cornstarch, ground cinnamon, and pinch of salt. Toss carefully until the blueberries are evenly coated. Pour the mixture into the prepared baking dish.
Step 3: In a separate medium bowl, prepare the crumble topping. Whisk together the all-purpose flour, rolled oats, brown sugar, granulated sugar, ground cinnamon, and salt.
Step 4: Add the cold, cubed butter to the dry topping ingredients. Use your fingertips or a pastry blender to cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces remaining.
Step 5: Evenly sprinkle the crumble topping over the blueberry filling in the baking dish. Ensure a good, consistent layer.
Step 6: Bake for 40-45 minutes, or until the topping is golden brown and the blueberry filling is bubbly around the edges. If the topping browns too quickly, you can lightly tent it with aluminum foil.
Step 7: Remove from the oven and let the fresh blueberry recipes crumble cool on a wire rack for at least 15-20 minutes before serving. This allows the filling to set properly. Serve warm with ice cream, whipped cream, or crème fraîche, or just enjoy it plain. For another comforting fruit dessert, consider trying The Ultimate Warm & Comforting Baked Peach Crumble.