Add sliced peaches, sugar, and salt to a saucepan and cook over medium heat a few minutes, just until the sugar dissolves and the peaches release their juice. Set aside. (Using canned peaches? Skip this step and use 1 quart jar, undrained.)
Preheat oven to 350°F.
Slice butter into a 9x13 inch baking dish and place in the oven while it preheats to melt. Remove once melted.
In a large bowl, mix flour, sugar, baking powder, and salt.
Stir in milk just until combined.
Pour over the melted butter and smooth into an even layer.
Spoon the peaches and juice over the batter.
Sprinkle generously with cinnamon.
Bake at 350°F for 38 to 40 minutes.
Serve warm with a scoop of vanilla ice cream.
Store leftovers covered in the fridge 4 to 5 days.
