2) Bring the cream and milk to a boil in a large heavy saucepan. Reduce the heat to low. Add the finely chopped chocolate and whisk until melted and very smooth. Remove from the heat.
3) In a large bowl, whisk the yolks until they are uniform in colour. Gradually whisk in half the hot chocolate mixture until very smooth. Once the eggs are slightly warmed in this way, gradually add the rest of the hot mixture, whisking continuously. Strain, if desired.
4) Divide the custard among eight (180ml) custard cups. Place the cups in a large baking pan and add enough hot water to the pan so that it comes halfway up the sides of the cups.
5) Bake until the custards are set, about 50 minutes. Remove from the water; chill for 3 hours.
6) To finish, top the custard with a layer of mini marshmallows. Use a kitchen blowtorch to evenly caramelize the tops of the marshmallow and garnish with the biscuits.