For the pastry:

1. Beat cream cheese and butter in the bowl of a stand mixer until smooth. Add the flour and salt and mix until a soft dough forms.
2. Form dough into two equal balls and flatten into disks. Wrap tightly in plastic wrap and refrigerate until firm, about 2 hours.

For the filling:

1. In a medium skillet, over medium heat, sauté mushrooms and onion with a sprinkle of salt until mushrooms have released their moisture and it has mostly evaporated. Stir in additional salt and pepper to taste. Add thyme and flour and cook for a minute.
2. Lower the heat and stir in sour cream. Remove from the heat and set aside. Cool to room temperature.

Turnovers

1. Preheat oven to 350°F.

2. On a floured surface, roll out one pastry disk to a thickness of 1/8 inch. Cut about 12 2 3/4-inch circles with a biscuit or cookie cutter. Roll dough scraps into a ball and flatten slightly, wrap and refrigerate.

3. Place a teaspoon of mushroom mixture on each pastry circle. Brush edges with egg. Fold over pastry and with a fork, press edges together to seal. Prick tops with a fork to let steam out. Transfer the turnovers to an ungreased cookie sheet.
4. Repeat with remaining dough. Re-rolling scraps and refrigerating as necessary to keep the dough workable.
5. Brush turnovers with egg. Bake about 12-15 minutes or until golden brown.