Make a fire or start some charcoal briquets for the Dutch Oven.
Melt butter in a skillet over medium heat.
Meanwhile, place berries in a large bowl. Using a potato masher, lightly mash the berries to release their juices. If the berries are really tart, sprinkle with sugar.
In another large bowl, whisk together flour, baking powder, and salt. Add sugar, milk, and vanilla extract; mix until well combined. Add the melted butter to the flour mixture; stir to combine.
Pour the batter into a Dutch oven with a liner.
Add the berries and their juices into the center. Sprinkle with sugar.
Place 6 coals under and 18 on top of the Dutch oven and check after 30 minutes.
Serve warm or at room temperature with whipped cream, or ice cream.