01 - Preheat oven to 375°F. Lightly grease a 2-quart baking dish with butter or cooking spray.
02 - Combine sliced peaches, raspberries, ½ cup sugar, cornstarch, lemon juice, and vanilla extract in a large bowl. Gently toss until fruit is evenly coated. Transfer to the prepared baking dish.
03 - Whisk together flour, ¼ cup sugar, baking powder, and salt in a medium bowl until thoroughly combined.
04 - Add cold cubed butter to the flour mixture. Using a pastry cutter or your fingers, work butter into flour until mixture resembles coarse crumbs with pea-sized butter pieces remaining.
05 - Whisk milk and egg together in a small bowl until blended. Pour over flour mixture and stir with a spatula just until dough comes together. Do not overmix.
06 - Drop spoonfuls of biscuit dough evenly over the fruit mixture, leaving some gaps for steam to escape. Sprinkle with coarse sugar if desired.
07 - Bake for 38 to 42 minutes until topping is golden brown and fruit filling is bubbly around edges. If topping browns too quickly, cover loosely with foil for final 10 minutes.
08 - Remove from oven and let cool for 10 to 15 minutes before serving. Serve warm with vanilla ice cream.