Preparation: 12 hours ahead
Prick each prune with a darning needle, put them in a bowl, cover with lukewarm water and leave to soak for 2 hours.
Bring ¼ litre (scant half pint) of water to the boil in a small saucepan. Take it off the heat, drop in the teabags and leave them to infuse, covered, for 15 minutes. Then remove the teabags and add 150 g (5½ oz) of sugar. Bring to the boil, and boil for 15 minutes, skimming frequently to remove any scum that rises to the surface.
After the prunes have soaked for 2 hours and are nicely swollen drain them and leave them to steep in the tea-syrup for 8–10 hours.
Finishing and serving the dish
Put a deep dish into the ice-making compartment of the refrigerator to chill.
Soften 50 g (1¾ oz) of butter. Whisk the whipping cream to a light snow. Incorporate the softened butter. Add the tablespoon of icing sugar and chill for 10 minutes. Meanwhile toast the slivered almonds lightly to a pale beige colour.
Dip a tablespoon into a bowl of hot water and use it to make 12 nicely shaped balls of cream; place them in the chilled dish. This must be done extremely fast. Put a prune on top of each ball of cream and cover it lightly with a spoonful of the tea-syrup. Sprinkle the slivered almonds over the top and serve very cold.