This is a nearly traditional salad in which the grapefruit plays a leading role, complementing mild shrimp and allowing you to make an almost ridiculously easy dressing, made up of nothing more than fish sauce (called nam pla in Thailand and nuoc mam in Vietnam), or soy, lime, a bit of sugar, and some water. Use good shrimp—Pacific or Gulf whites are the best, though the less expensive and widely available tiger shrimp are acceptable—and buy them big, because you’ll have fewer to peel.
The best way to retain the grapefruit’s juices is to peel and section it as you would an orange, not by cutting it in half and scooping out the flesh as you would to serve it at the table. Remove as much of the tough white pith as you can before cutting each section in two, which you should do just before assembling the salad.
