Chicken and leek pot pies

Name: Chicken and leek pot pies
Prep time: 20 min
Cook time: 1 h 15 min
Total time: 1 h 15 min
Yield: 8 portions
Ingredients: 2 - 3 leeks; 400 g water; 1 tbsp Chicken stock paste; 2 sprigs fresh flat-leaf parsley; 1 dried bay leaf; 700 g skinless chicken thigh fillets; ¼ tsp sea salt; ½ tsp ground black pepper; 200 g carrots; 50 g salted butter; 50 g plain flour; 2 tbsp Dijon mustard; 2 sprigs fresh thyme; ¼ tsp sea salt; ¼ tsp ground black pepper; 200 g pouring (whipping) cream; 2 sheets ready-made puff pastry; egg yolk