Amaretto sauce:
In the top of a double boiler over simmering water, stir together butter and sugar. Stir constantly until sugar and butter are dissolved and the mixture is very hot. Remove from heat. Whisk the egg well into the butter and sugar mixture. Continue whisking until sauce has come to room temperature. Add the amaretto liqueur.
To serve:
Preheat broiler. Cut pudding into 8-10 squares and place on a decorative oven proof serving dish. Spoon amaretto sauce over pudding and place under broiler until sauce bubbles. Serve immediately.