Combine blueberries, water, 1 cup white sugar, and 1 tablespoon butter in a saucepan; cook and stir over medium heat until heated through, about 5 minutes.
Transfer blueberry mixture to a deep 1 1/2 to 2-quart baking dish.
Beat 1/2 cup white sugar and 1 tablespoon butter together in a bowl until creamy. Sift flour, baking powder, and salt together in a separate bowl; stir into sugar-butter mixture.
Add milk; stir until incorporated.
Pour batter over blueberries.
Bake in the preheated oven until lightly browned and bubbling, about 30 minutes.
