From Fine Cooking, December 2011/January 2012
3 cups thinly sliced celery (about 3 medium stalks)
1-1/2 cups thinly sliced radishes (about 5)
3 Tbs. extra-virgin olive oil
1 Tbs. fresh lemon juice; more as needed
1/2 tsp. Dijon mustard
Kosher salt and freshly ground black pepper
1/4 cup coarsely chopped fresh flat-leaf parsley
Toss the celery and radishes in a large serving bowl.
Put the olive oil, lemon juice, mustard, 1/4 tsp. salt, and several grinds of black pepper in a small jar. Cover and shake to combine. Season to taste with more salt, pepper, and lemon juice.