Blitz the chocolate in the food processor and remove the lid.
Warm the milk and cream in a small saucepan. As it nearly reaches the boil, pour in the processor on top of the chocolate crumbs.
Allow to stand for 30 seconds then replace the lid and blitz for another 30 seconds. Then crack the egg down the funnel and blitz for another 45 seconds.
Remove the lid and add the chestnut puree and rum. Replacing the lid, pulse until combined.
Tumble the chopped dates into 6 verrine glasses or small pots.
Remove the processor blade and pour the batter into a jug before decanting carefully into your pots. Sprinkle over the crumbled meringues or amaretti if using.
Chill for at least one hour before serving.
Notes
Nigella says you can freeze these puddings for up to one week if you put them in ceramic pots and cover. Defrost them overnight in the fridge if you do this.