Place the milk and the cream in a saucepan and bring to the boil. Beat the egg yolks with the caster sugar until pale and fluffy. Pour the cream and milk over the egg and sugar mixture and return to the pan. Lower the heat and cook, stirring continually, until the liquid reaches 84°C (or coats the back of a spoon).
Pass the liquid through a fine sieve and then pour on to the chocolate (broken into small pieces). Mix well until the chocolate has melted and then pour into glasses. Place in the fridge and chill for at least 45 minutes.
Preheat the oven to 200°C.
Place the flour, butter, sugar and ground almonds in a bowl. Rub together with the tips of your fingers to obtain a crumble. Spread the mixture on to a baking sheet and cook for 10 to 15 minutes.
Place the egg yolks, cognac and the sugar in bowl and beat vigorously with an electric whisk until the mixture is pale and has tripled in volume (a sabayon).
Whisk the cream until thick. Mix the hazelnut praline into the sabayon and then carefully fold in the whipped cream.
Once the chocolate cream is set and well chilled, top with a quenelle of the cognac emulsion and sprinkle with a little crumble to serve.
«Prepare the crumble in advance to ensure that it is cool when served. Sprinkle it over the dessert at the very last moment to make sure that it keeps all its crunch.»