This refreshing salad with plenty of texture was inspired by a recipe in “Catalan Food” by Daniel Olivella. We soften and flavor the celery with a brief soak in a lemony vinaigrette, then toss it with parsley, frisée and toasted walnuts, which add richness and a little umami. The salad is great with grilled meats and seafood, hearty braises or even a platter of cured meats and cheeses.