Place the rinsed berries in a large cast-iron skillet or 9-inch round cake pan, and toss the berries with the sugar, cornstarch, cinnamon and lemon juice. Let them macerate for 20 minutes.
To make the crust, melt the butter on low in a pan, and then stir in the flour, sugar, baking powder, buttermilk, and salt. The dough will be slightly sticky, moist yet pliable.
Pat out the dough and place it over the berries.
Bake 40 minutes or until light brown and bubbling.