Covered in leathery green skin marked by spines, the plump, knobbly soursop (Annona muricata in Latin, guanábana in Spanish, and graviola in Portuguese—a term that's recently been co-opted by miracle-food hucksters) is as tasty as it is ungainly. Despite the name, its flavor is primarily sweet, a combination of apple, pineapple, and banana—to my palate, at least. I first tried it while living in Ghana and thence developed a mild obsession, culminating in a multi-day (successful!) guanábana search while on vacation in Colombia.
Native to the American tropics, and especially beloved in the Caribbean, South America, and Southeast Asia, soursop is closely related to the cherimoya and a slightly more distant cousin of the North American pawpaw, family connections easily observed when you split the fruits open—each features large, slick, dark seeds set at intervals in creamy, off-white-to-yellowish flesh. (A. murricata is also kin to the specific fruit known as "custard apple" and is sometimes erroneously called by that name, though "custard apple" is also an acceptable term for the entire Annona genus, in which case the label applies. It's complicated.)
If you're curious to try fresh soursop, look for it in markets in communities with large West Indian or Latin American populations; we've also spotted it in New York City's Chinatown. A ripe soursop is light yellowish-green in color (as opposed to an unripe one on the tree, which tends to be a truer, more uniform green) and, like a peach, will give a little when pressed with a finger. In my experience, fruits range in size from "large mango" to "your whole head." Store a ripe soursop in your fridge for up to a few days; though the skin will darken, the flesh will be just fine.
Soursop fruit is fibrous and juicy, and resists cutting into tidy cubes. The best way to enjoy a good specimen is to simply halve or quarter it, then dig in with a spoon, spitting out the seeds as you go.
If your soursop is overly stringy for your taste, or if you have more than you know what to do with, add it to milkshakes or smoothies, or purée it alone and press out the pulp to make juice. Beyond those basic uses, soursop flans, mousses, sorbets, and other custard-based or frozen treats are common in some Latin American countries; recipes abound on Spanish-language websites if you'd like to try your hand at something fancier. The Brooklyn ice cream shop Taste the Tropics makes a soursop ice cream that Daniel loves, as described in his local's guide to Brooklyn. However you're preparing it at home, do be careful to remove the seeds: Soursop is among several members of Annona whose seeds contain the neurotoxin annanocin, though it's unclear whether merely occasional consumption has any noticeable negative effects.
Sold in capsules under the name "graviola," soursop has also gained a faddish reputation of late as a cancer fighter, but there's not enough scientific evidence to back this up. I recommend ignoring any online hubbub around the medical benefits and focusing solely on its deliciousness—a demonstrably believable hype.