Thaw your puff pastry.
Dice up the bacon and cook it in a large oven safe pot on medium low heat. (see note)
Before the bacon crisps up, add your diced carrot and onions or leeks. Stir frequently to ensure nothing is burning. You can add a little broth if anything is getting too dark. Cook until the bacon is crisp, carrots are soft, and onion/leek is soft and darker in color.
Add your butter and once it melts, slowly add in the flour. Stir until well combined. Then, slowly add in your broth. Whisk until well combined.
Then, add in your milk and better than bouillon and whisk until they are combined.
Bring your heat to a boil and once it starts to boil, quickly lower the heat to low heat. Add in your chicken and frozen vegetables. You will see the mixture thicken up. Once the mixture is mixed well and very thick, turn off the heat and preheat the oven to 400F.
Roll out your sheet of puff pastry slightly, and cut into 25 3” squares. 5 rows down and 5 rows across.
Place puff pastry squares overlapping on top of the chicken bacon mixture in the skillet.
Mix one egg with water in a bowl. Using a pastry brush, brush a thin layer on top of the puff pastry.
Put it in the oven and bake for 25-30 minutes or until golden brown.