Prepare the Filling:
- Preheat the Oven: Preheat your oven to 375°F (190°C).
- Mix the Filling: In a large mixing bowl, combine the blueberries, granulated sugar, cornstarch, lemon zest, lemon juice, and vanilla extract. Toss until the blueberries are evenly coated.
- Transfer to Baking Dish: Pour the mixture into a greased 9×9-inch baking dish and spread it out evenly.
Make the Crumble Topping:
- Combine Dry Ingredients: In a medium bowl, combine the flour, oats, brown sugar, cinnamon, and salt. Mix well.
- Cut in the Butter: Add the cold, cubed butter to the dry mixture. Use a pastry cutter or your fingers to cut the butter into the mixture until it resembles coarse crumbs.
Assemble and Bake:
- Top with Crumble: Sprinkle the crumble topping evenly over the blueberry filling.
- Bake: Bake in the preheated oven for 35-40 minutes, or until the topping is golden brown and the filling is bubbling.
Cool and Serve:
- Cool: Let the blueberry crumble cool for 10-15 minutes before serving.
- Serve: Serve warm with a scoop of vanilla ice cream or a dollop of whipped cream for an extra treat!