Rinse the apples, remove the core, cut the apples into slices, sprinkle with the juice of one lemon.
Heat the butter in a frying pan. Briefly sauté the apple rings in it, spread the bread slices evenly on top and sauté for 2-3 minutes on each side over medium heat.
Serve the Poor Knights with cranberries. If desired, sprinkle with hail sugar and cinnamon.