For the gaufrette base
Melt the chocolate and the praline in a bain-marie. Remove from heat and add the waffle. Place in four 4 x 10 cm rectangular ring molds in a tin lined with parchment paper. Pour the mixture into the ring molds and place in the fridge until the mixture thickens and sets.
For the praline mousse
Heat the water and sugar in a pot until it reaches 120°C. In a mixer bowl combine the yolk and the syrup, adding gradually, and mix until fluffy. Heat the cream and praline in a saucepan stirring constantly until the praline melts. Soak the gelatin in water until soft and pliable. Strain the gelatin, add to the praline cream and mix until melted. Strain the cream and carefully fold into the egg mixture, using a spatula. Finally, fold in the whipped cream and mix carefully until all the ingredients have combined well. Lay the mousse over the gaufrette base and place the ring molds in the freezer. When chilled, remove from the ring molds and return to the freezer.
For the chocolate coating
Melt both types of chocolate in a bain-marie, remove from heat and add the crushed waffle. Consecutively dip the chilled wafers in the chocolate mixture ensuring they are well covered by the melted chocolate. Allow excess chocolate to drip off and place on a tray lined with parchment paper. Work quickly and return to the freezer until ready to serve. Before serving, return to room temperature for a few minutes so that the praline mousse becomes soft and creamy. They can also be stored in the fridge for up to 3 days.
For the chestnut ice-cream
Heat the milk and cream in a pot until just before boiling point. Mix the yolks and sugar in a bowl and gradually add the hot cream. Return mixture to the pot and cook over low heat, stirring with a spatula, until it reaches 82°C. Remove from the heat, strain through a fine sieve and allow cream to cool. Place in an ice-cream make according to the manufacturer’s instructions.