Heat the oven to 350°F and lightly grease a baking dish or cast iron skillet.
Add the sliced peaches to a large bowl with sugar, lemon juice, vanilla, cinnamon, and cornstarch. Stir until the peaches are evenly coated, then transfer to the prepared dish.
In a separate bowl, combine the flour, sugar, baking powder, and salt. Mix in the melted butter and milk until a smooth batter forms.
Spread the batter over the peaches and bake for 40 to 45 minutes, until the topping is golden and the peach filling is bubbling. Let cool slightly before serving.