To caramelize the onions, heat the butter over medium low heat in a heavy ovenproof skillet. Add the onions & cook for 20 minutes or so, stirring occasionally. When the onions are a deep golden color, remove from the pan and set aside.
To make the chicken, preheat the oven to 400 degrees. Combine the flour, salt, chili powder, thyme, allspice, and black pepper. Dredge each piece of chicken in the flour mixture, shaking off the excess.
In the same pan as the onions, heat the oil over medium high heat. Add each piece of chicken skin-side down and fry for a few minutes until golden brown; flip and cook for a few more minutes. Transfer to a plate.
Turn the heat down and let the oil cool off a little bit. Add the wine – this will definitely bubble and sizzle! Add the broth and simmer until the mixture is thickened slightly. Add the onions and chicken to the pan (skin side up) and bake for 20 minutes.
Remove from the oven, add the grapes, baste with the sauce, and bake for another 5-10 minutes. Top with parsley and serve with a green salad, bread, quinoa, rice, etc.