Preheat oven to 350 degrees.
Spray a square 8 inch baking dish lightly with cooking spray.
Melt butter in a small saucepan.
In a large bowl, whisk together flour, 1 cup sugar, baking powder and salt
Stir in milk until smooth and there are no lumps in the batter
Whisk in melted butter until smooth
Pour batter into prepared baking dish
Add blackberries evenly over batter ** see notes
Sprinkle with ¼ cup sugar, less or more if you like
Bake for 50-60 minutes or until golden brown
Remove from oven to wire rack and cool
Serve room temperature or warm with ice cream or whip cream if you like.