Preheat oven to 350 degrees F. Place butter in an 8-inch square baking dish. Melt butter in the preheating oven, about 5 minutes.
Remove from oven.
Place all of the batter ingredients in the baking dish and whisk together until mostly smooth. Scatter the berries over the batter.
Bake in preheated oven until a toothpick inserted into the center comes out clean, about 1 hour.
Notes
Don't spend too long trying to space out berries or do anything more than scattering them, because they actually shift during baking and your hard work will be ruined.Most of the time the berries join together in the center and leave a thick edge for the cobbler. If you want more berries, you can add up to ½ cup of more frozen berries when making the dish.Check on the baking dish about 10 minutes before the timer is set to go off, if the bread can have a toothpick come out clean, it's ready. You'll have berry juice on the toothpick but you don't want to see any batter goop. (Internal temp 200F degrees on an instant read thermometer).You don't need to thaw the berries. You can literally pull the berries out of the freezer as they are needed in the recipe and then toss them in the dish. It's so super easy! They thaw as they bake and turn out perfectly.