Preheat and prep the pan. Heat your oven to 375°F (190°C). Grease a 9-inch square baking dish or similar 2-quart baking dish with butter or nonstick spray.
Make the blueberry filling. In a medium bowl, combine blueberries, 1/2 cup sugar, cornstarch, lemon juice, and lemon zest.
Toss until the berries are evenly coated and glossy. Spread the mixture evenly in the prepared baking dish.
Mix the dry batter ingredients. In a separate bowl, whisk together the flour, 1/2 cup sugar, baking powder, and salt.
Add the wet ingredients. Pour in the milk, melted butter, and vanilla. Stir gently until just combined.
The batter should be thick but pourable; avoid overmixing.
Assemble the cobbler. Spoon the batter over the blueberries in rustic dollops. It doesn’t need to cover every inch—leave a few gaps so the fruit can bubble through. Sprinkle the top with coarse sugar if you like a slight crunch.
Bake until golden and bubbly. Bake for 35–45 minutes, until the topping is deep golden and the filling is bubbling around the edges.
If using frozen berries, add 5 minutes to the bake time.
Rest before serving. Let the cobbler sit for at least 10–15 minutes. This helps the juices thicken and makes it easier to scoop.
Serve warm. Add a scoop of vanilla ice cream or a dollop of whipped cream for a classic finish.