Start by preheating your oven to 350°F (175°C). In a large bowl, combine the sliced peaches, sugar, salt, cinnamon, lemon juice, and cornstarch. Gently toss everything together until the peaches are evenly coated. Set the mixture aside so the flavors can blend while you prepare the batter.
Place the butter directly into your baking dish and put it in the oven until completely melted. Keep an eye on it so it doesn’t brown. Once melted, carefully remove the dish from the oven and set it aside, leaving the butter inside.
In another mixing bowl, whisk together flour, sugar, baking powder, and salt. Slowly stir in the milk until the batter is smooth and lump-free. The consistency should be pourable but not too thin, similar to pancake batter.
Pour the batter evenly over the melted butter in the baking dish. Do not stir. Spoon the peach mixture evenly over the batter, including the juices. Again, avoid stirring—the batter will rise around the peaches as it bakes, forming the cobbler topping.
Bake for 35–45 minutes or until the top is golden brown and the peach filling is bubbling around the edges. If desired, sprinkle a little cinnamon on top before baking. Let the cobbler cool slightly before serving to allow the filling to thicken.