Preheat the oven to 350°F (175°C).

In a mixing bowl, combine the blueberries, sugar, lemon juice, and cornstarch. Toss gently to coat the blueberries.

Pour the blueberry mixture into a greased baking dish.

In another bowl, whisk together the flour, sugar, baking powder, and salt.

Add the milk and melted butter to the dry ingredients and stir until just combined.

Pour the batter over the blueberry filling in the baking dish.

Bake in the preheated oven for 30-35 minutes, or until the topping is golden brown and a toothpick inserted comes out clean.

Let cool for a few minutes before serving.