Preheat oven to 375°F (190°C).
Place the butter in a 9x13 inch baking dish and place in the oven to melt completely.
In a medium mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt.
Gradually stir in the milk until just combined; the batter should remain slightly lumpy.
In a separate bowl, toss the sliced peaches with lemon juice and cinnamon to prevent oxidation and enhance flavor.
Remove the baking dish from the oven. Pour the batter directly over the melted butter. Do not stir.
Spoon the peach mixture evenly over the batter. Do not stir.
Sprinkle the light brown sugar evenly over the surface of the peaches.
Bake for 40 to 45 minutes, or until the crust has risen to the top and is golden brown.
Allow to cool for 10 minutes before serving to let the juices thicken.