Preheat the Oven:

Preheat your oven to 375°F (190°C). Grease a 9x9-inch baking dish lightly with butter or cooking spray.

Prepare the Blackberry Filling:

In a large mixing bowl, combine blackberries, sugar, cornstarch, lemon juice, and vanilla extract. Stir until the blackberries are well-coated. Pour the mixture into the prepared baking dish, spreading it out evenly.

Make the Topping:

In another bowl, whisk together the flour, sugar, baking powder, and salt. Add the milk and melted butter, stirring until a smooth batter forms.

Assemble the Cobbler:

Spoon the batter evenly over the blackberry mixture. It doesn’t need to cover the blackberries completely; the topping will spread as it bakes.

Bake:

Place the dish in the preheated oven and bake for 35–40 minutes, or until the topping is golden brown and the blackberry filling is bubbling.

Cool and Serve:

Allow the cobbler to cool for about 10 minutes. Serve warm, topped with vanilla ice cream or whipped cream, if desired.