You can leave breasts whole or cut them up, whatever your preference. In a large skillet, heat oil over medium-high heat. Add chicken and pan-fry until cooked through and juices run clear, about 10 minutes. Remove chicken from skillet and set aside.
Using the same skillet, cook onion in butter until translucent but not brown, about 5 to 8 minutes. Season with paprika and salt. Pour chicken stock into the pan, and bring all to a boil. Reduce heat to simmer; mix flour with sour cream until smooth, then whisk into chicken stock. Place chicken in skillet; simmer until chicken is heated through and sauce has thickened.