Creamy Chicken Potpie

Name: Creamy Chicken Potpie
Ingredients: 4 teaspoons extra-virgin olive oil, divided; 1 pound boneless, skinless chicken breast, trimmed, cut into 1/2-inch cubes; 1 cup sliced shallots; 1 10- or 12-ounce bag frozen mixed vegetables (2-2 1/2 cups), thawed; ¼ teaspoon dried thyme; 2 cups reduced-sodium chicken broth, divided; ¼ cup cornstarch; ¼ cup reduced-fat sour cream; ¼ teaspoon salt; ¼ teaspoon freshly ground pepper; 6 sheets 9-by-14-inch phyllo dough, defrosted (follow package directions); Cooking spray (olive oil or canola oil)