In a medium mixing bowl, gently coat the blackberries with the granulated sugar and let them sit for 20 minutes.
Preheat the oven to 375 degrees F. Spray an 8 inch square pan with a non stick cooking spray.
In a separate bowl, stir together the flour, baking powder, salt, milk and vanilla extract. Then slowly mix in the melted butter. Be careful not to over mix. A few lumps are fine.
Pour the batter into the baking dish in an even layer.
Spoon the blackberry mixture on top of the batter. Do not stir the blackberries into the batter.
Bake for 45-55 minutes until the dough rises to the top and is golden brown.
Serve warm topped with ice cream or whipped cream. Enjoy!
Notes
Refrigerate the leftovers, covered, for up to 3-4 days.