Make the Mousse:

In a metal bowl set over a saucepan of simmering water combine the egg and the sugar and with an electric mixer beat the mixture at high speed for 3 minutes, or until it is thick and fluffy. Remove the pan from the heat and continue to beat the mixture set over the hot water for 3 minutes. Set the metal bowl in a bowl of ice and cold water, beat the mixture until it is cold, and stir in the macadamia nuts. In a chilled small bowl beat the cream with the until it just holds stiff peaks, stir one fourth of the whipped cream into the macadamia mixture until it is combined well, and fold in the remaining whipped cream. Spoon the mousse into 2 chilled desert glasses and chill them in the freezer for 25 minutes.

Make the Chocolate Rum Sauce:

In a small saucepan bring the cream and the rum to a boil, remove the pan from heat, and add the chocolate chips. Whisk the mixture until the choc- olate is melted and serve the warm sauce over the mousse.