Preheat Oven:
Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.
Prepare the Berries:
In a small bowl, whisk together sugar and cornstarch.
Place blackberries in a mixing bowl, drizzle with melted butter, and sprinkle the cornstarch mixture over the top.
Toss until the blackberries are evenly coated and spread them into the prepared baking dish.
Make the Batter:
In a mixing bowl, whisk together flour, sugar, baking powder, and salt until evenly blended.
Stir in milk, melted butter, and vanilla until combined but still slightly lumpy.
Pour the batter over the berries in the baking dish.
Bake:
Bake in the preheated oven for 55 to 60 minutes, until the berries are tender and the crust is golden brown.
Enjoy your delicious Blackberry Cobbler!