1. Butter the bottoms and sides of a 2-quart baking dish. Set aside.
2. In a medium bowl, combine blueberries, raspberries and strawberries. Sprinkle 1/4 cup sugar and cornstarch over berries and stir gently to combine. Set aside.
3. In a separate bowl, whisk self-rising flour and 1 cup granulated sugar together.
4. Pour in whole milk and melted butter and stir to combine.
5. Pour half the batter into the bottom of the prepared casserole dish. Place berries onto batter, evenly spreading each type of berry across the batter. Spoon remaining batter evenly on top of the berries, covering as much of the berries as possible. Sprinkle top of batter with 1 tbsp of granulated sugar.
6. Bake for 50 minutes. (Optional: Sprinkle top of cobbler with 1 tbsp Betty Crocker Cupcake Gems Gold Sugar for decoration). Bake another 10 minutes or until golden brown and the fruit is hot and bubbly. Remove from oven and allow cobbler to rest for at least 30 minutes before serving.
7. Serve warm with a scoop of vanilla ice cream, if desired.