Preheat the oven to 150 C / Gas 2. Butter 6 to 8 small ramekins and place them in a baking dish, and pour hot water into the dish around them.
Wash the raspberries carefully, and dry them on kitchen paper. Bring the milk to the boil with the vanilla extract in a saucepan.
Whisk together the whole eggs with the egg yolks and caster sugar until pale and smooth. Pour in the hot milk in a thin stream, whisking constantly. Pour the custard mixture into the ramekins, and add 3 or 4 raspberries on top of each one.
Bake in the preheated oven in the water bath until golden, about 40 minutes. Let cool slightly, then remove from water bath. Chill in the fridge for at least 2 hours before serving.
Decorate with any remaining raspberries, just before serving.