01 - Preheat 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 pinch of salt. Toss until berries are evenly coated.
03 - Spread the blueberry mixture evenly in the prepared baking dish.
04 - In a separate bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well blended.
05 - Pour melted butter, milk, and vanilla extract into the dry ingredients. Stir until just combined—the batter will be thick and slightly lumpy. Do not overmix.
06 - Drop spoonfuls of batter evenly over the blueberry filling, covering most of the surface while leaving small gaps for steam to escape and fruit to bubble through.
07 - Bake for 40 to 45 minutes until the topping is golden brown and set, and the berry filling is bubbling around the edges.
08 - Let the cobbler rest for at least 15 minutes to allow the filling to set. Serve warm with vanilla ice cream or whipped cream if desired.