This salad goes all-in with the mushroom flavor, while salty pecorino and crunchy celery provide balance. Tearing the shiitakes into pieces makes for easier prep, and the jagged edges get nicely brown when sautéed.
5 tablespoons extra-virgin olive oil, divided
1 tablespoon plus 2 tsp. red wine vinegar
About 1 tsp. kosher salt, divided
About 1/4 tsp. freshly ground pepper
1/2 cup celery leaves, torn into pieces
2 1/2 cups thinly sliced celery, cut on a diagonal
1 1/2 cups baby spinach leaves
3/4 cup flat-leaf parsley leaves
12 ounces fresh shiitake mushrooms, stems removed, caps torn into 1-in. pieces
1/3 cup hazelnuts, toasted and chopped
1 1/2 ounces pecorino cheese, shaved with a vegetable peeler
How to Make It
In a small bowl, whisk together 4 tbsp. oil, the vinegar, 3/4 tsp. salt, and 1/4 tsp. pepper and set aside.
Put celery leaves, celery, spinach, and parsley in a salad bowl.
Heat remaining tbsp. oil in a 12-in. frying pan over medium-high heat until shimmering. Add mushrooms and cook undisturbed until browned on underside, 1 to 2 minutes. Season with 1/4 tsp. salt and cook, stirring occasionally, until browned and tender but not too soft, 2 to 3 minutes.
Transfer mushrooms to bowl with celery, add vinaigrette and hazelnuts, and toss to coat. Scatter cheese over salad, season to taste with more salt and pepper, and toss again.