Preheat the oven to 350°F and lightly butter a 9x13 baking dish.
In a large bowl, toss the berries with sugar and lemon juice, then spread them evenly in the dish.
In another bowl, whisk together flour, baking powder, salt, milk, and melted butter until smooth.
Pour the batter over the berries, letting it settle without stirring.
Bake for 40-45 minutes, or until the top is golden and a toothpick comes out clean.
Let it cool slightly before serving. Best enjoyed warm with a scoop of vanilla ice cream.