Prepare a 9x9 cake pan with nonstick cooking spray or butter and set aside.
In a small saucepan, melt butter. Once the butter has melted, add the sugar and stir until dissolved, remove from the heat and pour into the bottom of your prepared baking dish.
Next, top with fresh blueberries, and set aside.
In a medium bowl, prepare the cake batter according to the directions on the packaging. Pour carefully over the blueberries in an even layer.
Bake for 35-45 minutes, or until a toothpick is inserted into the center of the cake, comes out clean. Allow it to cool on a wire rack before serving.
Top with whipped cream, vanilla ice cream or any of your other favorite toppings.