Preheat the oven to 375°F (190°C).
In a medium bowl, toss the blueberries with 1/4 cup of sugar and lemon juice. Transfer the mixture to a 9x9-inch baking dish.
In a separate large bowl, whisk together the flour, the remaining 3/4 cup of sugar, baking powder, salt, and cinnamon.
Stir in the milk and melted butter until a smooth batter forms.
Spoon the batter evenly over the blueberries in the baking dish. Do not stir.
Bake for 40 to 45 minutes, or until the topping is golden brown and the blueberry juices are bubbling around the edges.
Remove from the oven and let cool for at least 15 minutes to allow the sauce to thicken before serving.