Grease an ovenproof dish. Wash the plums, cut them in half, stone them and put them into the mould. Sprinkle with 1 tablespoon sugar and plum water. Preheat oven (electric cooker: 175°C/circulating air: 150°C/gas: level 2).
Score the vanilla pod lengthwise and scrape out the pulp. Separate the eggs. Beat the egg whites until stiff, then add 50 g sugar. Chill the beaten egg whites. Whisk the egg yolks, vanilla pod, 50 g sugar and 1 pinch of salt until creamy.
Alternately stir in flour, cream and milk. Fold in the beaten egg white in two portions.
Pour egg mixture over the plums. Bake in a hot oven for about 30 minutes. Cover with aluminium foil to prevent the surface from turning too brown. Remove the clafoutis from the oven, dust with icing sugar and serve warm.
Whipped cream tastes good with it.