Divide the crushed amaretti biscuits between six lightly greased ramekin dishes (custard cups).
Drizzle the liqueur over.
Whisk the egg yolks and 30 ml/2 tbsp caster sugar together until thick and pale.
Warm the milk, cream and almond essence together.
Whisk into the egg yolk mixture.
Stand the bowl over a pan of hot water and stir over a moderate heat until the custard thickens.
Do not allow it to boil or it will curdle.
Pour the mixture over the crushed biscuits and leave to cool, then chill.
Sprinkle the almonds over, then cover completely with caster sugar.
Place under a hot grill (broiler) until the sugar has caramelised.
Leave to cool, then chill again until ready to pack.