Add all ingredients to a temperature proof mixing glass and stir briskly for 30 seconds. Pour into a tea cup and serve. To serve hot, water must be very hot, as all other ingredients are room temperature or lower. Top with ground nutmeg (sub ground cinnamon).
To make buttered syrup: Combine 1 cup each of sugar, brown sugar and butter in a saucepan. Cook over low heat, stirring occasionally, until butter is melted (6-8 min). Add 1.5 cups vanilla ice-cream, and stir, scraping saucepan often until smooth (1-2 min). Store refrigerated up to 2 weeks or frozen up to one month.