Wash and stone the plums and cut them into slices. Spread the plums in an ovenproof dish and pour 2 tablespoons of port wine over them. In a preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see
manufacturer) for approx. 25 minutes, remove and reduce the oven heat (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see manufacturer). Place plums in a sieve, collecting the liquid. Put the liquid and 50 ml port wine in a pot and bring to the boil.
Mix 2 tablespoons of water and starch, add to the liquid, bring to the boil again and simmer for about 1 minute. Add the plums to the sauce and let them cool down.
Grate cheese. Put 150 g of grated cheese, cream and mustard in a pot, melt cheese in it at low heat while stirring. Remove from the heat and let it cool down a little.
Mix eggs, season with salt and pepper. Stir carefully into the cheese mixture. Spread the cheese mixture on 6 greased, ovenproof moulds (each containing 150 ml) and sprinkle with the rest of the cheese.
Place the ramekins in the fat pan of the oven. Fill up with boiling water until the ramekins are halfway through the water. Leave in the oven for 25-30 minutes. Remove from the oven and remove the rim immediately with a small knife.
Let the cheese cream cool for 15-20 minutes, then turn out onto 1 plate at a time. Garnish with plum sauce and watercress.