In a large mixing bowl, combine the berries, lemon juice, vanilla, cornstarch and sugar. Mix well to coat the berries evenly and set aside.
To make the topping, mix the flour, sugar, baking powder and salt together. Using your hands or a pastry cutter, mix 1½ sticks of the butter into the dry ingredients until it looks like coarse crumbs. Pour the cream in and mix until the dough just comes together, taking care not to overmix (it should be slightly sticky but manageable).
In a 10-inch cast-iron skillet, melt the remaining butter over medium-low heat. Add the berry mixture and cook gently until heated through, about 5 minutes. Drop the dough by spoonfuls over the warm berries, covering the surface as much as possible. Bake about 30-40 minutes, until the top is lightly browned and the fruit is bubbling. Serve warm.