Preheat the oven to 350 degrees and prepare an 8x10 baking dish by greasing with nonstick cooking spray.
In a large bowl, whisk together the flour, 1 ½ cups sugar, baking powder, and salt.
Add the butter and stir to combine.
Whisk in the milk until the batter is smooth.
Pour the batter into the prepared baking dish.
Add the blueberries over the top of the batter and sprinkle the sugar over the top of the cake.
Bake in the preheated oven for one hour, until the cake is set in the center and a toothpick inserted into the cake comes out clean.
Serve warm or at room temperature.