01 - Preheat the oven to 375°F (190°C).
02 - In a large bowl, toss peaches with granulated sugar, lemon juice, ground cinnamon, ground nutmeg, and cornstarch until the fruit is thoroughly coated.
03 - Transfer the coated peaches to a 9x13-inch baking dish, spreading them evenly.
04 - In a separate bowl, whisk together all-purpose flour, granulated sugar, baking powder, and salt.
05 - Add cold, cubed unsalted butter to the flour mixture and blend using a pastry cutter or fork until the mixture resembles coarse crumbs.
06 - Pour in whole milk and vanilla extract. Stir just until the dough comes together; avoid overmixing.
07 - Drop spoonfuls of dough evenly over the peaches, leaving small gaps for steam release.
08 - Sprinkle coarse sugar over the biscuit topping if using.
09 - Bake for 40 minutes, or until the biscuit topping is golden brown and the filling is bubbling at the edges.
10 - Allow to cool for at least 15 minutes before serving. Enjoy warm, optionally topped with vanilla ice cream.