Famous Gordon Ramsay Chicken Sandwich

Ingredients

• 3 tablespoons chopped dill pickle or cornichon
• 1 celery stalk, chopped fine
• 500g roasted chicken pieces (from one large bird)
• 1 tablespoon fresh dill, finely minced
• 1 green onion, thinly sliced
• 75g coarsely chopped walnuts
• 160g thick sour cream or yogurt
• 1 tablespoon vinegar or lemon juice
• 2 teaspoons Dijon-style mustard
• 160g mayonnaise (whole egg preferred)
• ¾ teaspoon kosher or cooking salt
• ½ teaspoon powdered onion
• ¼ teaspoon powdered garlic
• ¼ teaspoon black pepper
• Soft white bread slices (use around 20, older bread works better)
• Generous spread of salted butter