01 - Preheat oven to 375°F. Lightly grease a 9x9-inch baking dish with butter or cooking spray.
02 - Combine frozen blueberries, granulated sugar, cornstarch, lemon juice, ground cinnamon, and salt in a large bowl. Toss until berries are evenly coated. Spread mixture in the prepared baking dish.
03 - Whisk together flour, sugar, baking powder, baking soda, and salt in a separate bowl until well combined.
04 - Pour melted butter, milk, and vanilla extract into the flour mixture. Stir until just combined; the batter will be thick. Avoid overmixing to prevent tough texture.
05 - Drop spoonfuls of batter evenly over the blueberry filling. Cover most of the surface while leaving small gaps for steam to escape and fruit to bubble through during baking.
06 - Bake for 40 to 45 minutes until the topping is golden brown and fully cooked, and the berry filling is bubbling around the edges.
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 whipped cream if desired.