Begin by cooking and shredding the chicken, and preparing the mixed vegetables.
In a skillet, sauté diced onion in butter until translucent
Add flour to the skillet to create a roux, and cook for a minute to eliminate the raw flour taste.
Gradually add chicken broth and milk, stirring to create a creamy sauce.
Mix in shredded chicken and mixed vegetables into the creamy sauce, creating the pot pie filling.
Cut puff pastry sheets into small rounds and place them in mini muffin tins. Fill each pastry cup with the chicken and vegetable mixture.
Cover each mini pie with another puff pastry round, creating a top crust.