01 - Preheat oven to 375°F. Lightly grease a 9-inch baking dish and set aside.
02 - In a large mixing bowl, toss the mixed berries with pure maple syrup, vanilla extract, cornstarch, lemon juice, and a pinch of salt until the berries are evenly coated. Transfer the mixture to the prepared baking dish, spreading it into an even layer.
03 - In a separate large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until well combined.
04 - Add the cold cubed butter to the flour mixture. Using a pastry cutter or your fingertips, quickly work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
05 - In a small bowl, whisk together the whole milk, maple syrup, and vanilla extract. Pour the wet mixture into the flour-butter mixture and stir gently just until combined. Be careful not to overmix, as this will make the topping tough.
06 - Drop spoonfuls of the cobbler dough evenly over the berry filling, leaving some gaps for the berries to bubble through as they bake.
07 - Bake for 35 to 40 minutes, or until the topping is golden brown and the berry filling is bubbly and thickened around the edges.
08 - Remove from the oven and let the cobbler cool for 10 minutes before serving. Serve warm with vanilla ice cream or whipped cream if desired.