1. About two hours before serving, process cream cheese, flour and 1/2 cup of butter in a food processor till smooth.
2. Shape into a ball, wrap and refrigerate for at least one hour.
3. In skillet over medium heat, cook mushrooms and onions in 3 tbsp butter till tender.
4. Add salt, basil and flour, stir together, add sour cream. Stir until thickened. Set aside.
5. On a floured surface with a floured rolling pin, roll half of dough 1/8-inch thick.
6. With floured 21/2-inch round cookie cutter, cut out as many circles as possible.
7. Repeat with other half of dough.
8. Preheat oven to 450°F.
9. Onto one-half of each dough circle, place a tsp of mushroom mixture.
10. Brush edges of circle with some egg; fold dough over filling.
11. With fork, firmly press edges together to seal; prick tops.
12. Place turnovers on un-greased cookie sheet; brush with remaining egg.
13. Bake 12 to 15 minutes till golden. Serve warm.