Preheat oven to 400°F (200°C).

1. In an oven-safe skillet (preferably cast iron), melt the butter over medium heat. Add the sugar and cook, stirring occasionally, until the mixture turns a light amber caramel, about 5–7 minutes.
2. Arrange peach slices over the caramel in a circular pattern. Cook for 5–10 minutes until the peaches start to soften. Add lemon juice or cinnamon if desired.
3. Roll out the puff pastry on a lightly floured surface and cut it to fit the skillet. Carefully place it over the peaches, tucking in the edges around the fruit.
4. Transfer the skillet to the oven and bake for 25–30 minutes, or until the puff pastry is golden and puffed.
5. Remove from oven and let rest for 5 minutes. Place a serving plate over the skillet and carefully invert the tart onto the plate.
6. Serve warm or at room temperature with vanilla ice cream or whipped cream, if desired.