01 - Preheat oven to 375°F. Lightly grease a 9x9-inch baking dish with butter or cooking spray.
02 - Combine frozen blueberries, sugar, cornstarch, lemon juice, cinnamon, and salt in a large bowl. Toss until berries are evenly coated. Spread mixture in 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 gently until just combined—batter will remain thick. Avoid overmixing to prevent tough texture.
05 - Drop spoonfuls of batter over the blueberry filling, distributing evenly across the surface. Leave small gaps between dollops to allow fruit juices to bubble through during baking.
06 - Bake for 40 to 45 minutes until topping is deep golden brown and set, and fruit filling is actively bubbling around edges.
07 - Let cobbler rest for at least 15 minutes before serving to allow filling to set. Serve warm with vanilla ice cream or whipped cream if desired.