Bountiful Blueberry Cake

1 quart blueberries, fresh or frozen (use 2 quarts to
    make recipe in a 13 x 9-inch pan)
1/2 cup granulated sugar (or use firmly packed
    brown sugar or raw sugar for added richness)
1 (18.25 ounce) box cake mix (lemon, white, yellow
    or pineapple flavor)
1/2 cup butter, or more as required

Preheat oven to 350 degrees F. Lightly grease a 9-inch square baking dish.

Place blueberries into prepared baking dish; sprinkle sugar evenly over berries.

Sprinkle the dry cake mix, right out of the box, over berries. Cut the margarine in thin slices to cover top of cake mix. If necessary, during baking add more margarine so the entire top of cake is moistened.

Bake 55 to 60 minutes. Serve warm or cold, with or without ice cream or milk.