Brown chicken pieces in olive oil and butter then remove to reserve bowl
Remove all but 1 tbl. butter and oil
Add onions, shallots, garlic, bouquet garni - sautee till limp
Add chicken and 3 tbl. sherry wine vinegar
Cook for 25 minutes covered
Remove chicken and keep warm in oven
Add remaining 3 tbl. vinegar, chicken stock, tomato paste, mustard, and tarragon. Bring to a boil and simmer to reduce
Remove from heat and add cream
Over low flame cook down to good creamy sauce
Pour over chicken and serve