In a medium bowl, mix together the cream cheese and 1 cup of butter until well blended. Mix in the flour until fully incorporated. Pat into a ball, and refrigerate while you make the filling.
Melt butter in a large skillet. Add the mushrooms and onion. Season with thyme, salt and pepper. Cook and stir until tender, about 5 minutes. Sprinkle the flour over everything so it won't get lumpy, then reduce the heat to low, and stir in the sour cream. Heat just until thickened, then remove from the heat.
Preheat the oven to 350 degrees F (175 degrees C). On a lightly floured surface, roll the dough out to about 1/4 inch thickness. Cut into 3 inch rounds. Place a small amount of the mushroom mixture on one side of each circle, then fold the dough over and press to seal. Prick the tops with a fork to vent steam, and place the pastries on a baking sheet. (They can also be frozen at this time until needed.)
Bake for 15 minutes in the preheated oven, or until golden brown. If baking frozen turnovers, it may take an additional 5 minutes.