Saute onions, celery, carrots garlic, and mushrooms in butter in a large saucepan over medium heat.
Stir in flour, thyme, poultry seasoning, salt and pepper. Cook for 1 minute, stirring constantly.
Slowly stir in chicken broth and cream. Constantly stir mixture until smooth, creamy and thickened.
Add nutmeg, cooked chicken, and frozen peas. Combine well.
Ladle mixture into 6 individual small loaf tins.
Cut puff pastry to cover each tin. Cover tin with puff pastry and press down around rim to adhere.
Brush puff pastry with melted butter. (Optional, I think it makes the pastry look prettier).
Place tins on baking sheet and bake at 400 for 15-20 minutes or until tops are golden.