Chicken pan pie

Ingredients

• 1 tablespoon vegetable or olive oil
• 500 grams chicken thigh fillets, cut into 2 cm pieces
• 1 medium brown onion, finely chopped
• 1 small carrot, finely chopped
• 2 sticks celery, finely chopped
• 300 grams button mushrooms, quartered
• 1 clove garlic, crushed
• 1 cup cream
• 2 tablespoons worcestershire sauce
• 2 teaspoons finely chopped thyme
• 1 sheet frozen puff pastry, thawed
• 1 egg, lightly beaten
• 2 tablespoons shredded parmesan
• 1 teaspoon poppy seeds
• mashed potato, to serve