In large pot, melt the butter over low heat. Add leeks, carrot, onion, celery, and chicken. Stir gently, cover to cook over low heat for 5 minutes.
Take off the lid, stir the vegetables, turn the chicken. cover and cook another 5 minutes or until chicken is done.
Remove the chicken and set aside.
Sprinkle the flour over the vegetables and pan juices. Stir to cook over low heat for 2 minutes. Slowly add white wine and 4 c broth. Stir and cook until bubbly and thickened. Add the sour cream very slowly and allow to cook gently.
Slice the chicken into bite size pieces and add back to pot.
Bring the 4 remaining cups of stock to boiling and add fideo. Cook until almost done. Add all to the soup. Bring back to boiling and serve immediately.