Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.

Prepare the filling: In a large bowl, gently toss the peaches with the 3/4 cup sugar, cornstarch, cinnamon, nutmeg, and lemon juice until evenly coated. Pour the mixture into the prepared baking dish.

Prepare the topping: In a separate medium bowl, whisk together the flour, 1/4 cup sugar, baking powder, and salt. Cut in the cold, cubed butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.

Stir in the 1/2 cup of milk until just combined to form a shaggy dough. Do not overmix. Drop spoonfuls of the dough evenly over the peach filling, leaving small gaps for the peaches to bubble through.

Brush the tops of the biscuit dough lightly with the remaining 1 tablespoon of milk and sprinkle generously with turbinado sugar for a crunchy crust.

Bake for 40 to 45 minutes, or until the topping is golden brown and the peach filling is thick and bubbling actively around the edges. If the topping starts browning too quickly, loosely cover with foil.

Let cool on a wire rack for at least 20 minutes before serving warm, ideally with vanilla ice cream or whipped cream.