In a large braiser or dutch oven, melt butter over medium-high heat. Season chicken with salt and pepper. Sauté chicken about 2-3 minutes per side until brown. Transfer to a plate and set aside.
Into the pot, add onions and brown sugar; season with salt and pepper, sauté for 5 minutes. Add garlic and allspice. Cover and sauté until onions tuns golden brown, stirring occasionally, for another 5 minutes.
Add bay leaves and mustard. Deglaze the pot with chicken stock. Add chicken, then beer and vinegar. Bring to boil. Reduce heat to medium. Simmer, covered for 8 to 10 minutes. Uncover and let it simmer until the sauce thickens, 15-20 minutes. Season with salt and pepper.
Sprinkle with parsley.
Recipe by Flavor and Friends at http://flavorandfriends.com/braised-chicken-in-amber-ale-and-sweet-onion/