Place heavy cream and sugar in the blender. Select MANUAL/SPEED LO and blend, gradually increasing the speed to HI until cream is just whipped, 15-20 seconds. Do not overmix. Remove about ½ cup of whipped cream from blender, set aside in a bowl and refrigerate.
Add all remaining ingredients to blender and blend on MANUAL/SPEED 5 until blended, about 15 seconds. Chill eggnog in refrigerator in blender jar for at least 1 hour. Just before serving, add reserved whipped cream to blender and PULSE 2 to 3 times. Pour eggnog into cocktail glasses. Garnish with additional grated nutmeg and serve immediately.