Mix ingredients together in a blender (except the Angostura), pour into a highball glass and stir with a cinnamon stick. Leave refrigerated for an hour or longer. Pour into another glass topped with ice and add a dash of Angostura bitters. Garnish if desired.
A jug makes 4-5 servings dependent on the shape of the jug... so multiply accordingly on the amount of thirsty guests you have. (1.5 fl oz = 30 ml or 1 standard pour).