Spring greens chicken pie

Name: Spring greens chicken pie
Cuisine: American
Ingredients: 1 roll of puff pastry; 300g pre-cooked chicken breast; 1 leek; 1 shallot; 1 courgette; 100g frozen peas; Handful of chopped kale or spinach; 2 cloves of garlic; 1 tsp Fresh thyme; 1 tsp Fresh tarragon; 2 tbsp half fat crème fraiche; 1 lemon; 1 chicken stock cube; 1 tbsp Plain flour; 20g Parmesan; 1 egg; 1 tsp mustard