Preheat oven to 400˚F.
In a small mixing bowl whisk together the egg and water; set aside.
On a lightly floured working surface, roll out the pastry sheet into a 12-inch square; cut the square into 16 small squares; set aside.
Melt butter in a 10-inch oven-safe skillet set over medium heat.
To the melted butter add onions, carrots, and celery; cook for 4 minutes.
Stir in the diced turkey.
Sprinkle flour over the mixture and stir it around; continue to cook for 2 more minutes while constantly stirring.
Pour in the broth and continue to stir.
Add in the cream and peas; bring mixture to a boil.
Continue to cook for 3 to 4 minutes, or until the mixture thickens.
Season with thyme, salt, and pepper; taste for salt and adjust accordingly.
Remove from heat.
Arrange previously cut puff pastry squares on top of the turkey mixture, each square slightly overlapping so that the entire surface of the creamy mixture is covered.
Using a pastry brush, brush the squares with previously prepared egg wash.
Optionally, sprinkle the top with sea salt.
Bake for 20 to 25 minutes, or until mixture is bubbly and top is browned.
Remove from oven. Let stand 10 minutes.
Sprinkle with fresh thyme leaves and serve.