Preheat the oven to 350°F (177°C). Lightly grease an 11x7-inch baking dish that is at least 2 inches deep.
Add the sliced peaches directly to the prepared baking dish.
Sprinkle the brown sugar, granulated sugar, cinnamon, nutmeg, cornstarch, and salt over the peaches. Drizzle the vanilla extract and lemon juice over the top.
Using a rubber spatula, gently stir until the peaches are evenly coated, then spread them into an even layer.
In a medium mixing bowl, whisk together the melted butter, granulated sugar, egg, sour cream, sourdough discard, and vanilla extract until smooth.
Add the flour, baking powder, baking soda, salt, and cinnamon. Stir just until combined. Do not overmix. The batter will be thick.
Drop spoonfuls of the batter evenly over the peaches. Using the back of a spoon or a small offset spatula, gently spread the batter over the fruit. It doesn't have to completely cover the peaches, and a few peaches peeking through are perfectly fine.
Sprinkle the coarse raw sugar evenly over the top.
Place the baking dish on a parchment-lined baking sheet to catch any bubbling juices during baking.
Bake for 45–50 minutes, or until the topping is golden brown, the peach filling is bubbling around the edges, and the center of the topping reaches about 200–205°F if checking with an instant-read thermometer.
Allow the cobbler to cool for at least 20 minutes before serving. The filling will continue to thicken as it cools.
Serve warm with vanilla ice cream or whipped cream.
Notes
Recipe Tips
Use fresh or frozen peaches. There’s no need to thaw frozen peaches before adding them to the baking dish.
Add extra cornstarch for juicy peaches. Increase the amount to 2½ tablespoons if using especially juicy fresh peaches or frozen peaches.
Don’t overmix the topping. Stir the batter only until the ingredients are combined.
Leave the peach skins on if you prefer. They’ll soften during baking, so peeling is optional.
Use a baking sheet underneath the dish. This will catch any peach juices that bubble over.
If you don't have an 11 x 7-inch baking dish, you can also use a 10-inch cast iron skillet.
How to Store and ReheatStore leftover cobbler covered in the refrigerator for up to 4 days.Reheat individual servings in the microwave for 20–30 seconds, or warm the entire cobbler in a 325°F oven until heated through.You can also freeze leftover cobbler for up to 3 months. Allow it to cool completely, wrap it well, and freeze. Thaw overnight in the refrigerator before reheating.