The leftover vinaigrette is delicious on greens or roasted vegetables.
Whisk together vinegar, mustard, and shallot in a small bowl. Gradually add oil in a steady stream and whisk until combined thoroughly. Season with salt and pepper.
Combine celery stalks and leaves, escarole, and pine nuts in a large bowl. Season with salt and pepper. Drizzle with 3 tablespoons vinaigrette; toss to combine. Vinaigrette can be made 2 days ahead and stored in refrigerator.