While most celery recipes focus on the tender hearts, this crisp, refreshing salad makes a point to use up the whole bunch, including the oft-overlooked leaves. The recipe comes to us from Georges Testa, the third-generation owner of Le Moulin Bleu confectionery and tearoom in Provence. Like many locals, Testa observes Christmas with a meal called either the repas maigre (“lean meal”) or, paradoxically, the gros souper (“big supper”), which consists of seven meatless dishes such as brandade de morue, vegetable gratins, and a whole poached fish. This celery salad dressed with a simple mustard vinaigrette always makes an appearance on Testa’s holiday table but would serve as an excellent side dish any time of year.