Instructions:
1. Preheat your oven to 375°F (190°C).
2. In a mixing bowl, combine the blackberries, 1 cup of sugar, and lemon juice. Gently toss the blackberries until they are coated in the sugar and lemon juice mixture.
3. In a separate bowl, whisk together the flour, 1 cup of sugar, baking powder, and salt.
4. Add the melted butter, milk, and vanilla extract to the dry ingredients. Stir until the batter is well combined and smooth.
5. Grease a 9×9-inch baking dish or a similar-sized ovenproof dish.
6. Pour the blackberry mixture into the greased baking dish, spreading it out evenly.
7. Pour the batter over the blackberries, spreading it out to cover the fruit.
8. Place the baking dish in the preheated oven and bake for 45-50 minutes, or until the top is golden brown and the blackberry mixture is bubbling.