Preheat your oven to 350°F (175°C) to ensure it reaches the correct temperature by the time you're ready to bake. While the oven is heating, take an 8-inch square baking dish and grease it thoroughly with butter or non-stick spray to prevent the cobbler from sticking. This step ensures even cooking and easy cleanup.
In a large mixing bowl, combine 1 cup of sugar with 1 cup of flour. Whisk these dry ingredients thoroughly to ensure they are well mixed and free from lumps. This step is crucial for achieving the right texture in your cobbler batter. Next, stir in 1 cup of whole milk and 1 teaspoon of vanilla extract until the mixture is smooth and creamy.
The addition of butter should be done last; cut it into small pieces and gently fold it into the batter using a spatula to avoid overmixing. Ensure the batter is evenly distributed throughout the bowl.
In a medium mixing bowl, gently toss the blackberries with the remaining 1/2 cup of sugar until evenly coated. This step ensures that the berries will be sweetened properly without becoming too soggy. Make sure to handle the berries carefully to avoid bruising them, which can lead to a less appealing cobbler.
Place the cobbler dish in the preheated oven and bake for exactly 1 hour, or until the top is a rich golden brown and the filling is bubbling vigorously. Keep an eye on it towards the end to prevent over-browning. You'll know it's done when you see the crust starting to crack and the juices are bubbly.
Avoid opening the oven door frequently as this can cause the cobbler to settle rather than rise properly.
Once baked, remove the cobbler from the oven and let it cool on a wire rack for at least 10 minutes. This cooling period is crucial as it allows the juices to thicken slightly and makes the cobble easier to handle. Serve warm with a dollop of whipped cream or a scoop of vanilla ice cream. Enjoying it too soon can result in a soggy crust, so be patient!