Chicken casserole

Name: Chicken casserole
Ingredients: 4 chicken breasts; 2 onions, 1 roughly chopped, 1 thinly sliced; 1 carrot, roughly chopped; 1 celery stalk, roughly chopped; 6 whole peppercorns; 1 fresh bay leaf; Water, to cover; 55g/2oz butter; 30g/1oz plain flour; Salt and freshly ground black pepper; 1 small head broccoli, cut into florets and blanched; 1 free-range egg yolk, lightly beaten; 2-3 tbsp double cream; Squeeze lemon juice; 1 tbsp chopped fresh parsley, to serve; Boiled baby carrots, to serve