Preheat the oven to 350°F and spray a 10-inch cast-iron skillet with nonstick cooking spray.

In a medium bowl, combine sugar, flour, baking powder, salt, and milk. Slowly whisk in the melted butter. Pour the batter into the skillet.

Add the sliced peaches, brown sugar, cornstarch, and cinnamon to a saucepan over medium heat and stir to combine, simmering for 2-3 minutes until sugar is dissolved and peaches are softened slightly. Add the peach mixture evenly over the top of the batter.

Bake for 45 minutes. Line a baking sheet with aluminum foil and place it on the bottom of the oven to catch any drips.

After 45 minutes, sprinkle the turbinado sugar over the top and return to oven. Bake an additional 10-15 minutes, or until golden brown.

Serve topped with ice cream or whipped topping.