Preheat your oven to 375°F (190°C).
In a large bowl, combine blackberries and 1/2 cup of sugar.
Transfer the blackberry mixture to a greased baking dish.
In another bowl, mix flour, baking powder, salt, and remaining sugar.
Add milk, melted butter, and vanilla extract to the dry ingredients.
Stir until just combined; do not overmix.
Pour the batter over the blackberries in the baking dish.
Bake for about 45 minutes or until the top is golden brown.
Let it cool slightly before serving.
Enjoy warm, optionally with a scoop of ice cream!