Preheat the oven to 350 degrees. Spray a 13x9 baking dish with baking spray and set aside.
In a large bowl, combine the berries, sugar, lemon juice, cornstarch and vanilla. Toss gently to coat.
Transfer the berries to the bottom of the baking dish and spread evenly.
In another medium sized bowl, combine the flour, sugar, baking powder and salt. Stir to combine. Add in the diced butter and using forks or a pastry cutter, cut the butter into the dry ingredients until it’s about pea-sized.
Add in the milk and continue to cut the mixture until it is combined and holds its shape when pressed together. It should be a little on the dry side.
Sprinkle the topping over the berries in the baking dish. Sprinkle with the additional turbinado sugar, if desired.
Bake in the preheated oven for about 50 minutes or until the mixture is bubbly and the topping is slightly browned. Allow to cool slightly before serving.