01 - Preheat your oven to 375°F and lightly grease a 9x9-inch baking dish with butter or cooking spray.
02 - In a large bowl, combine frozen blueberries, sugar, cornstarch, lemon juice, cinnamon, and salt. Toss until berries are evenly coated, then transfer to the prepared baking dish and spread in an even layer.
03 - In a separate medium bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well combined.
04 - Pour melted butter, milk, and vanilla extract into the dry ingredients. Stir gently until just combined; the batter will be thick. Avoid overmixing to prevent toughness.
05 - Drop spoonfuls of the batter evenly over the blueberry mixture, covering most of the surface while leaving some gaps for steam to escape and fruit to bubble through.
06 - Bake for 40 to 45 minutes until the topping is golden brown and cooked through, and the berry filling is bubbling around the edges.
07 - Let the cobbler cool for at least 15 minutes to allow the filling to set. Serve warm with vanilla ice cream or whipped cream.