Chicken salad - Donnafugata

Ingredients

• Half a large chicken (800-900 gr, 1 1/2 to 2 lbs)
• 1 onion
• 1 celery stalk
• 1 carrot
• small bunch of parsley
• 1 clove garlic
• 1 heart cos lettuce
• 1 heart young white celery
• 1 ripe tomato
• 3 salted anchovies
• 2 tablespoons extra-virgin olive oil
• 1 teaspoon Dijon mustard
• juice of 1/2 a lemon
• salt and pepper