Preheat the oven to 375°F (190°C)
Grease a baking dish
In a bowl, combine blueberries, sugar, lemon juice, and cornstarch
Pour the blueberry mixture into the baking dish
In another bowl, mix flour, sugar, baking powder, and salt
Cut in cold butter until the mixture is crumbly
Stir in milk until just combined
Drop spoonfuls of the batter over the blueberries
Sprinkle sugar on top if desired
Bake for 35 to 45 minutes until golden and bubbly
Let cool slightly before serving