Salt and pepper skin side of chicken thighs. Heat a heavy stainless steal pan, reduce heat to medium and put in chicken skin side down to brown and render chicken fat. Chicken will stick at first, do not touch as skin browns and fat renders chicken will free itself. Salt and pepper meat side of chicken. Turn over and brown meat side.
Remove chicken from pan and set aside under foil. Add carrots, celery, onion, mushrooms and garlic to pan, salt & pepper to taste and saute until softened (5-7 minutes).
Deglaze pan with sherry and add bay leaf. Increase heat to high and reduce 50%.
Add mustard and stir to mix well.
Return chicken to pan skin side up. Add broth sufficient to cover chicken two-thirds. Bring to boil, cover reduce heat and simmer 45 minutes until chicken is fall off the bone tender.
Mean while make a slurry with corn starch. When chicken is done, uncover and stir in just enough of slurry to slightly thicken sauce till it coats a spoon. Cook one to two minutes so starch looses raw taste.
Add sour cream and stir in well. Remove from heat and taste sauce. Adjust salt & pepper as needed.
Serve two thighs with a small mound of grits, polenta, mashed potatoes, couscous or egg noodles.