Preheat oven to 350°F with a rack in the center of the oven. Lightly grease an 8x8 baking pan.
In a large bowl, gently stir together all filling ingredients. Transfer to the prepared pan.
Topping (see note):
In a medium bowl, combine sugar, flour, baking powder, and salt. Add the vanilla extract and melted butter and stir until fully combined. The mixture will resemble a cross between a crumb topping and a sugar cookie dough.
Press pieces of the topping together with your fingers to form flat irregular shaped pieces. Place the pieces of topping all over the top of the blackberries. Bake for 30-35 minutes, until the berries are bubbling and the topping is beginning to turn light golden brown. Place the pan on a wire rack to cool for about 15 minutes; the juices will thicken up a bit as it cools.
Notes
*Use a mix of any berries. I used strawberries, blackberries, raspberries, and blueberries. Halve or quarter the strawberries. If your berries are really juicy you can increase the flour in the berry mixture to 4 tablespoons or ¼ cup.TOPPING: If you prefer your cobbler a little heavier on the topping, use the following measurements for the topping portion of the recipe. Preparation and bake time will be about the same.