This chilly treat is an adaptation of one served at the Royale Eatery, a burger and shake shop in Cape Town, South Africa. A simple purée of avocado, ice cream, mint leaves, and ice, it's sweet, rich, and dense enough to stand a spoon in. For a thinner drink, add an additional half cup of ice cubes. This recipe first appeared with Seánan Forbes' web-exclusive story Cape Town Classic.