• Step 1: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with butter or non-stick cooking spray.
• Step 2: In a large bowl, combine the blackberries, sugar, cornstarch, cinnamon, and nutmeg. Toss gently to coat the berries. Pour the mixture into the prepared baking dish.
• Step 3: In a separate bowl, whisk together the flour, baking powder, and salt. Cut in the chilled butter using a pastry blender or two forks until the mixture resembles coarse crumbs. Stir in the cold milk just until a soft dough forms.
• Step 4: Drop the dough by large spoonfuls onto the top of the blackberry mixture, covering the surface as evenly as possible.
• Step 5: Bake for 35-40 minutes, or until the topping is golden brown and the fruit is bubbling. Allow the cobbler to cool for at least 15 minutes before serving.