01 - Preheat the oven to 375°F. Lightly grease a 2-quart baking dish.
02 - In a large bowl, combine sliced peaches, raspberries, ½ cup sugar, cornstarch, lemon juice, and vanilla extract. Gently toss to coat. Transfer mixture to the prepared baking dish.
03 - In another bowl, whisk together flour, ¼ cup sugar, baking powder, and salt.
04 - Add cold, cubed butter to the flour mixture. Cut in the butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
05 - In a small bowl, whisk together milk and egg. Pour over the flour mixture and stir until just combined (do not overmix).
06 - Drop spoonfuls of the biscuit topping evenly over the fruit. Sprinkle with coarse sugar, if using.
07 - Bake for 38–42 minutes, until the topping is golden and the fruit is bubbling. If the topping browns too quickly, cover loosely with foil for the last 10 minutes.
08 - Remove from oven and let cool slightly before serving. Enjoy warm, optionally with vanilla ice cream.