For the chocolate espuma:
2 tablespoon crème de menthe
4 ounce cooking chocolate, grated or chopped very fine
2 tablespoon heavy cream
For the Drink:
4 ounce white rum
2 ounce Kahlua
1 cup ice cubes
Chocolate curls to decorate with
To make the chocolate espuma, heat the cream till it is just about to boil. Remove from heat and add the crème de menthe. In a bowl, put the cooking chocolate and pour the heavy cream concoction on top of it. Cover and let stand for 5-6 minutes. Remove the lid and stir briskly until the concoction is melted and glossy. Beat for 2-3 minutes, and then put in a whipped cream dispenser. Charge with a cream nitrous charger and then shake vigorously. Remove the cream charger and cap tightly. Keep in the fridge for at least one hour. To make the drink, in a tall martini glass, pipe half the chocolate concoction at the bottom of the glass, making sure it forms a small mound at the bottom. Combine the white rum with the Kahlua with plenty of ice cube in a cocktail shaker, and carefully strain half of it in the glass, avoid pouring it directly on top of the chocolate espuma. Serve immediately, decorated with chocolate curls. Then curls and the cream chargers work well together.
If you want to make simply the chocolate espuma it is great to let it cool fully. The nitrous from the cream chargers is held in place both by the cream (as is standard with whipped cream) and also the cooling chocolate.