Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch glass or ceramic baking dish.
Pour the entire contents of both cans of peaches (including the heavy syrup) directly into the baking dish. Spread them into an even layer.
If using cinnamon, sprinkle it evenly over the peaches.
Open the box of dry yellow cake mix and sprinkle it evenly over the entire layer of peaches. Do not stir! Gently pat it down to level it out.
Place the thin slices of cold butter evenly across the entire surface of the dry cake mix, covering as much of the powder as possible.
Bake uncovered on the center rack for 45 to 55 minutes, or until the filling is vigorously bubbling and the top crust is a deep golden brown.
Remove from the oven and let rest for 10-15 minutes before serving warm with a scoop of vanilla ice cream.