01 - Preheat oven to 375°F and lightly grease a 2-quart baking dish with butter or cooking spray.
02 - In a large bowl, combine sliced peaches, raspberries, ½ cup sugar, cornstarch, lemon juice, and vanilla extract. Gently toss until fruit is evenly coated.
03 - Pour the fruit mixture into the prepared baking dish and spread into an even layer.
04 - In a separate bowl, whisk together flour, ¼ cup sugar, baking powder, and salt until well combined.
05 - Add cold, cubed butter to the flour mixture. Use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
06 - In a small bowl, whisk together milk and egg until blended.
07 - Pour the milk and egg mixture over the flour-butter crumbs. Stir gently with a spoon just until combined - do not overmix as this will toughen the biscuits.
08 - Drop spoonfuls of the biscuit dough evenly over the fruit filling, leaving some spaces for steam to escape. Sprinkle with coarse sugar if desired.
09 - Bake for 38-42 minutes until the biscuit topping is golden brown and fruit filling is bubbling around the edges. If topping begins to brown too quickly, cover loosely with aluminum foil for the final 10 minutes.
10 - Remove from oven and let cool for at least 15 minutes before serving. Serve warm, topped with vanilla ice cream if desired.