Preheat oven to 375 degrees
Pour the melted butter into a 13 x 9 inch baking dish.
In a medium bowl, combine the flour, 1 cup sugar, the baking powder, and the salt and mix well. Stir in the milk, mixing until just combined. Pour this batter over the butter, but do not stir them together.
In a medium pot, combine the berries, lemon juice, vanilla extract, cornstarch, & sugar and bring to a boil, stirring constantly.
Pour the berries over the batter, but do not stir them together.
Bake in the preheated oven for 40-45 minutes or until the top is golden brown.
Serve warm or cold plain or with your favorite topping.