Carefully wash and core each apple, cutting them into slices ~⅛" thick on the outer edge.
In a large nonstick pan over low heat, add the butter. While it melts, mix the sugar, cinnamon (if using), and vanilla together in a small bowl.
Then arrange the apple slices in a single layer in the pan, then raise the heat to medium-low for 5 minutes (6 if considering the time spent layering the apples), until the apple juices have mostly dissipated.
Then sprinkle half the sugar mixture over the apple slices, flip the slices over and turn the heat down to low, then cook for 3 more minutes.
Flip the apple slices one more time and then sprinkle on the rest of the sugar mixture and cook for 7-10 more minutes, keeping heat low, until the apple slices finish browning.