Prepare the Fruit Filling: Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish. In a large bowl, gently toss the sliced peaches and raspberries with the sugar, cornstarch, lemon juice, vanilla extract, cinnamon, and salt until the fruit is evenly coated. Let the mixture sit for 10–15 minutes to allow the juices to release and the cornstarch to activate, which will help thicken the filling during baking.
Spread the Fruit in the Dish: Pour the fruit mixture into the prepared baking dish, spreading it evenly with a spatula. Try to distribute the raspberries throughout so every bite has a mix of both fruits, and avoid pressing down too firmly to maintain the natural texture of the peaches.
Mix the Dry Ingredients: In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well combined. This ensures even distribution of the leavening agents, which will help the biscuit topping rise properly and become light and fluffy during baking.
Cut in the Butter: Add the cold, cubed butter to the dry ingredients and use a pastry cutter or your fingers to work it in until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining. These butter pockets will melt during baking, creating those irresistible flaky layers in the topping.
Add Wet Ingredients: Stir in the milk and vanilla extract just until the dough comes together and is moistened. Do not overmix or the topping will become tough and dense; it should be slightly lumpy and sticky, which is perfectly normal for a drop biscuit batter.
Drop the Topping Over Fruit: Using a large spoon or ice cream scoop, drop dollops of the biscuit batter evenly over the fruit filling, leaving small gaps between each mound to allow for expansion. Don't spread the batter smooth; the rustic, uneven surface will brown beautifully and create crispy edges.
Add Optional Sugar and Bake: If desired, sprinkle the coarse sugar over the biscuit topping for extra crunch and a sparkling finish. Bake for 35–40 minutes, or until the topping is golden brown and the fruit filling is bubbling vigorously around the edges, indicating that the cornstarch has thickened the juices.
Cool and Serve: Remove the cobbler from the oven and let it rest for 15–20 minutes before serving. This resting time allows the filling to set slightly, making it easier to scoop without being too runny. Serve warm with a generous scoop of vanilla ice cream or a dollop of freshly whipped cream for the ultimate summer dessert experience.
