Preheat the oven to 350°F (175°C).

In a mixing bowl, combine the blackberries, half a cup of sugar, and vanilla extract. Let this mixture sit for about 10 minutes.

In another bowl, whisk together the flour, baking powder, salt, and remaining sugar.

In a separate bowl, mix the milk and melted butter.

Pour the wet ingredients into the dry ingredients and stir until just combined.

Spread the batter evenly in a greased 9-inch baking dish.

Spoon the blackberry mixture over the batter.

Bake in the preheated oven for 40-45 minutes or until the top is golden brown.