In a bowl, sprinkle crushed rosemary, rubbed sage, salt, and pepper over chicken. Toss to coat. Heat olive oil in a large non-stick dutch oven. Add chicken to oil, and cook until chicken is done. About 7-8 minutes. Remove chicken to a bowl. Set aside.
Melt butter in the remaining oil in pot. Add onion, celery, carrot and garlic and saute about 3-4 minutes, stirring occasionally.
Add flour all at once and mix well. Cook for another 3-4 minutes, stirring constantly. Add half-and-half, broth, and chicken base. Continue stirring constantly until mixture thickens and comes to a boil. About 10 minutes.
Reduce heat and add chicken and remaining seasonings to taste. Cook an additional 5 minutes.