Take your 4 chicken breasts, place them on a cutting board and pound to 1/4 thickness. (I put Cling Wrap over the chicken to prevent splatter) Spread cream cheese on half of the chicken breast. Then on top of cream cheese, spread 1/8 cup of spinach. Fold the chicken breast over.
Take 1 sheet of the Puff Pastry and unfold. Cut into 4 squares. Take each square and roll out with a rolling pin and a little flour. Place the stuffed chicken breast in the center of the rolled Puff Pastry. Fold the bottom over the chicken, then wet the sides with a tiny amount of water and fold in. Wet the top and fold as well. Place on a baking sheet and brush with milk.
Bake at 350 for about 35 minutes or until crust is golden brown.