01 - Preheat oven to 375°F. Lightly grease a 9x9-inch baking dish with butter or cooking spray.
02 - In a large bowl, combine frozen blueberries, granulated sugar, cornstarch, lemon juice, cinnamon, and salt. Toss until berries are evenly coated. Spread mixture in the prepared baking dish.
03 - In a separate medium bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well blended.
04 - Pour melted butter, milk, and vanilla extract into the dry ingredients. Stir gently with a spatula just until combined. The batter will be thick and slightly lumpy—avoid overmixing.
05 - Drop spoonfuls of the batter evenly over the blueberry filling. Leave small gaps between portions to allow fruit juices to bubble through during baking.
06 - Bake for 40 to 45 minutes until the topping is golden brown and set, and the berry filling is bubbling vigorously around the edges. If the top browns too quickly, tent loosely with foil.
07 - Let the cobbler rest for at least 15 minutes before serving to allow the filling to set. Serve warm with vanilla ice cream or freshly whipped cream.