Preheat oven to 350°F (175°C). Place the melted butter in a 9x13-inch baking dish.
In a medium bowl, mix the flour, granulated sugar, baking powder, and salt. Gradually stir in the milk until a smooth batter forms.
Pour the batter evenly over the melted butter in the baking dish, but do not stir.
Arrange the peach slices evenly over the batter. Sprinkle brown sugar and cinnamon on top.
Bake in the preheated oven for 40-45 minutes, or until the top is golden brown and the batter has risen around the peaches.
Serve warm with a scoop of vanilla ice cream if desired.