Celery Root Rémoulade

Name: Celery -Root Rémoulade
Ingredients: 3/4 cup well-shaken buttermilk; 2 teaspoons cornstarch; 1/2 teaspoon salt; Pinch of cayenne; 1 large egg yolk; 1 1/2 teaspoons extra-virgin olive oil; 1 tablespoon chopped fresh flat-leaf parsley; 1 tablespoon chopped fresh tarragon; 1 anchovy fillet, rinsed, dried, and finely chopped; 1 tablespoon chopped cornichon (French sour gherkin); 1 tablespoon drained capers, rinsed; 1 teaspoon finely chopped shallot; 1/2 teaspoon Dijon mustard; 1/2 teaspoon sugar; 2 to 3 teaspoons fresh lemon juice; 2 tablespoons water; 1 (1-pound) celery root, peeled and coarsely shredded