1 Preheat oven to 400°F.
2 Roast garlic: Remove the papery outer layers of the garlic bulb, leaving intact the skins of the individual cloves. Cut 1/4 to a 1/2 inch off the tops of cloves, exposing the individual garlic cloves.
Place the head of garlic on a piece of aluminum foil. Drizzle some olive oil over the garlic, and sprinkle it with salt and pepper.
Wrap the head of garlic with the aluminum foil and place in the oven. Bake for 45 minutes, or until the flesh of the cloves are light brown and feel quite soft when pressed. Set aside to cool. (See how to roast garlic.)
3 Brown the chicken pieces: While the garlic is roasting, heat a tablespoon of olive oil in a large, heavy-bottomed pot (with lid) or Dutch oven, on medium high heat. Rinse the chicken pieces in cold water then pat dry with paper towels. Season liberally with salt and pepper.
Brown the chicken pieces, starting them skin-side down, cooking them a few minutes on each side, working in batches so that you don't crowd the pan.
4 Cook onions until soft: While the chicken is browning, peel and quarter the onions. Remove chicken from pan when nicely golden with tongs or a slotted spoon and set aside on a plate. Discard any fat and oil beyond about 1 Tbsp left in the pan.
Put the onions in the pot and cook them until softened, stirring frequently, about 5 minutes.
5 Add tomatoes, herbs, chili powder, chicken, wine, then simmer: Add the tomatoes to the pot, the thyme, bay leaves, and ground chile powder. Put the chicken pieces on top of the tomatoes. Pour in the wine and bring to a simmer.
Cover and cook on medium-low heat for 40 minutes, stirring from time to time so that the vegetables don't stick.
6 Crush roasted garlic: After the garlic has cooled enough to handle, squeeze out the roasted garlic from the cloves into a small bowl and crush with a fork.
Sprinkle with salt and pepper to taste. Set aside to serve with the chicken stew.
7 Add mustard, thicken sauce: When the chicken has cooked, add the mustard to the pot and stir to blend. Increase the heat to medium-high and cook uncovered for 10 more minutes, or until the sauce is thick enough to cling to the meat. Remove bay leaves. Salt and pepper to taste.
Serve stew over rice or pasta, with the garlic paste on the side.