Chicken pot pie | New Idea

Ingredients

• 4 tablespoons butter
• 1/4 cup onion, chopped
• 1/4 cup celery, chopped
• 1/4 cup carrot, chopped
• 1/4 teaspoon salt
• 2 tablespoons flour
• 2 cups milk
• 1/2 cup heavy cream
• 1 chicken stock cube
• 2 cups chicken, cooked and chopped
• 1/2 cup frozen peas
• 1/2 teaspoon fresh thyme plus more for garnish if desired
• 1 sheet frozen puff pastry
• 1 egg, beaten slightly with a fork