The ingredients for this cool, crisp salad are available all winter long. The anchovies may be omitted, if desired.
Chop anchovies and place in a bowl with mustard. Add 1 tablespoon of the lemon juice and pepper to taste, and mix well. Slowly whisk in the olive oil. The dressing can be made a day ahead of time.
Peel the celery to remove the strings. Cut each stalk into thirds and julienne. Set aside. Quarter and core the apple, but do not peel. Thinly slice each quarter and place in a serving bowl. Sprinkle remaining 3/4 teaspoon lemon juice over apples and toss to coat.
Julienne endive leaves. Add celery and endive to the apples and toss with dressing. Season to taste with salt and pepper. Serve immediately.