PREPARE pie pastry according to recipe directions. Chill 30 minutes.
HEAT butter and oil in medium saucepan over medium heat. Add onion; cook 5 minutes or until tender. Stir in flour, seasoned salt, thyme and pepper until blended. Stir in chicken broth gradually until blended. Stir in cream. Bring to a boil over medium-high heat, stirring constantly, cooking until sauce thickens. Remove from heat. Stir in chicken and vegetables until coated with sauce.
HEAT oven to 425°F. Roll larger ball of dough on a lightly floured work surface into a 13-inch circle. Place in 9 1/2-inch deep dish glass pie plate for the bottom crust. Fill pie crust with chicken filling. Roll out remaining dough. Place dough carefully on top of filled pie. Trim edges of dough leaving a 3/4-inch overhang. Fold top edge under bottom crust. Press edges together to seal and flute as desired. Cut several 1/2-inch slits in top crust to vent steam.
BAKE 30 to 35 minutes or until crust is golden brown. Let stand 15 minutes before serving.