Remoulade Sauce

Ingredients

• 1 large egg yolk
• 3 tablespoons Dijon- or Creole-style mustard
• 1/4 cup white-wine vinegar
• 1 tablespoon paprika
• 1 cup vegetable oil
• 2 tablespoons grated horseradish, fresh or prepared
• 1 teaspoon finely chopped garlic
• 13 cup finely chopped scallions
• 13 cup finely chopped celery
• 2 tablespoons finely chopped parsley
• 2 tablespoons ketchup
• Salt and freshly ground black pepper to taste