Combine the sliced peaches, sugar, and salt in a saucepan and stir until the fruit is coated evenly. The sugar will start pulling moisture from the peaches almost right away, which is exactly what you want.

Set the pan over medium heat and cook for a few minutes, then take it off the heat once the sugar has dissolved and the peaches have released their juices. The mixture should look glossy and lightly syrupy, not dry or grainy.

Heat the oven to 350 degrees F, place the sliced butter in a 9x13 inch baking dish, and set the dish in the oven while it preheats. Pull the dish out as soon as the butter is melted and before it starts browning or smelling nutty.

Whisk the flour, sugar, baking powder, and salt in a large bowl, then stir in the milk just until a smooth batter forms and pour it over the melted butter. The batter should spread easily into an even layer and look like a thin pancake batter.

Spoon the peaches and their juices over the batter and scatter ground cinnamon generously across the top. Leave the layers alone and let some open spots remain, so the batter has room to rise up around the fruit.

Bake for about 38 to 40 minutes until the top is golden and the fruit is bubbling around the edges. You’ll know it is ready when the kitchen smells like cinnamon and caramelized peaches and the center no longer looks pale.