I invented this salad a few years ago on a freezing January in Boston when I was desperately trying to think of something vibrant and fresh to serve at a friend's baby shower. Something to offset the usual selection of doughy, starchy finger sandwiches and cookies. I remember feeling rather discouraged by the limited selection of mid-winter produce. Finally I picked up some firm, deeply magenta heads of radicchio, a few shiny ruby grapefruits and, on a whim, a chunk of pecorino pepato and a bag of walnuts. I wasn’t really sure where I was going with all this but it just felt right. (You're probably saying “grapefruit with cheese?!” but I swear, it’s delicious.)