Sadly there will only ever be two or three weeks a year when this salad can be made, that brief period when strawberries have not quite finished but raspberries have begun.
Beat the egg yolks and sugar together until they are creamy and thick. Boil the cream and milk with the vanilla pod, then pour into a blender and process.
Pour on to the egg and sugar whisking all the time. Stir over a low heat until the texture first loosens and then thickens slightly, showing it has cooked.