01 - Preheat oven to 375°F. Lightly grease a 2-quart baking dish.
02 - In a large bowl, combine peaches, raspberries, sugar, cornstarch, lemon juice, vanilla extract, and salt. Toss gently until the fruit is evenly coated.
03 - Pour the fruit mixture into the prepared baking dish and spread into an even layer.
04 - In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
05 - Cut the cold butter into the flour mixture using a pastry cutter or your fingertips until it resembles coarse crumbs.
06 - In a small bowl, whisk together the milk and egg. Pour into the flour mixture and stir just until combined — do not overmix.
07 - Drop spoonfuls of the biscuit dough over the fruit filling, leaving small gaps for steam to escape.
08 - Bake for 40 minutes, or until the topping is golden brown and the fruit juices are bubbling.
09 - Let cool for at least 15 minutes before serving. Serve warm, optionally topped with vanilla ice cream or whipped cream.