In a skillet, heat the olive oil and sauté the mushrooms and thyme in high heat. Wait until all of their water has evaporated and stir constantly until well browned. Add the bacon and the leeks and continue cooking in medium heat until leeks are tender. Set aside.
In a pot, heat 3 tablespoons olive oil with the flour until flour starts to smell nutty. Remove from heat and gradually add the milk half a cup at a time, stirring constantly. (It will get really thick at first, but this will break any lumps that may form. As you continue adding milk, it will loosen up).
Return to a medium heat and whisk until it thickens. It will be almost like a pudding. When thickened remove from heat and add the cheese, cinnamon, nutmeg, salt and pepper. Taste and adjust seasonings.
Fill with the filling and top with the other sheet of puff pastry. Cut the excess and pinch edges to seal them.
Let pie rest for 15 minutes, invert onto a rack/plate, remove pan and re-invert onto another plate.
Serve with a green salad. Eat.
You can boil the chicken, or buy a rotisserie one. I prefer to butterfly two half breasts, pound them to even their thickness and cook them with a tablespoon or two of olive oil in a skillet until browned from each side. In the same skillet, without cleaning it, I then cook the mushrooms and leeks.
If you have any leftover puff pastry, just cut it in strips, sprinkle them with some cheese (or a cinnamon-sugar mixture) and bake them until brown for a tasty, crunchy snack!