Preheat oven to 400F.Dry the chicken by patting with paper towels and if you haven't Pre-seasoned, sprinkle both sides liberally with salt and pepper.
Place the flour in a shallow bowl and dredge the chicken in the flour to coat.
In a large, ovenproof pan (12-inches will do), heat the oil over medium-high heat. Add the floured chicken in three batches (don't overcrowd the pan) and brown lightly for 3 to 5 minutes on each side.
Remove the browned thighs, set aside and continue with the rest until all the chicken is browned and set aside.
Drain any excess fat from the pan and add the chopped pancetta and cook until crispy.
If necessary, remove from the pan, set aside and drain the excess fat (without wiping the pan). Reduce heat to medium-high. Add the bacon back to the pan along with chopped onion and cook until soft, but not brown.
Add the garlic and cook another minute.
Add the mushrooms and saute until soft.
Add the sherry. Raise the heat to high, bring to boil, scraping the bottom of the skillet to mix the brown bits into the liquid. Cook another 2 minutes to cook down the alcohol.
Add chicken stock and parsley. Return chicken to the skillet, skin side up. Bake for 35 minutes (or until an instant-read thermometer is about 165 degrees), the chicken should be very tender.
Remove the chicken and set aside. With a fork, mash together the butter and 3 tablespoons of flour and add it to the sauce.
Return to the stove, stirring constantly, over medium-high heat until the sauce is thickened slightly.
Taste for seasoning and season to taste, put the chicken back in the sauce, and serve hot.
When browning the chicken don't overcrowd the pan. Overcrowding the pan will cause the chicken to steam instead of brown.
Don’t have sherry? Try replacing it with white wine or vermouth.
Omitting alcohol from the recipe – Sherry adds a delicious complexity this sauce, but if you don’t cook with alcohol, to deepen the flavor, try breaking up a bouillon cube and a tablespoon of lemon juice at the end for extra flavor.