Preheat oven to 350 F. Rinse blueberries and mix with 1/2 cup granulated sugar, cornstarch and lemon juice. Spread blueberries into a greased baking dish.
In a large bowl, whisk together flour, sugar, salt and baking powder. Whisk in milk, melted butter and vanilla extract, whisk until smooth.
Pour the batter over the blueberries and bake for 50-55 minutes.