Deseed the melon. Use a ball cutter to cut out balls or cut the melon into slices, peel and dice the flesh. Wash plums, halve, stone and cut into slices.
Heat butter in a frying pan. Add the cinnamon stick. Fry the plums briefly all around, remove. Sprinkle sugar in the pan and caramelise while stirring. Deglaze with orange juice, bring to the boil and simmer for about 5 minutes while stirring until the caramel has dissolved.
Carefully mix in the plums and melon. Remove from the pan with the stock. Mix crème fraîche and vanilla sugar. Wash the lemon balm, shake dry, cut the leaves into strips.
Serve the plums and melon with the caramel and vanilla-crème-fraîche Sprinkle with lemon balm.