3 tablespoons lemon juice, plus more to taste
1/2 teaspoon fine sea salt, plus more to taste
Freshly ground black pepper
1/4 cup extra-virgin olive oil
3 large fennel bulbs, thinly sliced on a mandoline
2 Granny Smith apples, halved and cored, thinly sliced on a mandoline
1/3 cup fennel fronds or roughly chopped parsley leaves
1/2 cup toasted walnuts
2 1/2 ounces Parmesan, shaved with a vegetable peeler (about 2/3 cup)
In a small bowl, whisk together lemon juice, salt and pepper. Slowly drizzle in oil, continuously whisking, until dressing is emulsified. Taste and add more lemon juice and/or salt if needed.
In a large bowl, toss the dressing with fennel, apple and celery. Fold in fennel fronds or parsley and walnuts. Top with Parmesan just before serving.