A Sunday Bloody Mary will be absolutely transformed with a straw made from the stem, or one of the frilly leaves as a garnish, not to mention a leaf or two, finely chopped and added into the tomato.
Cole Slaw, with the leaves cut into strips similar to the cabbage, or even sliced kale or kohlrabi leaves will add so much savory flavor, and not much heat.
Make a bright spring soup. Asparagus, pea, etc. Just before serving, add a handful of the chopped horseradish leaves, stir in, and serve. The leaves will wilt and offer a hint of darker, more complex flavor against all that Spring brightness.