Begin by preheating the oven to 400°F. Prepare the garlic by trimming the top of the bulb, exposing the tips of the cloves while keeping the skins intact. Place the garlic bulb on a square of aluminum foil, drizzle generously with olive oil, and sprinkle with salt and pepper. Wrap tightly and roast in the oven for 45 minutes, until the cloves are golden brown and yield easily when pressed. Set aside to cool.

While the garlic roasts, heat a tablespoon of olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Rinse the chicken pieces under cold water, then pat them thoroughly dry with paper towels. Season all sides liberally with salt and freshly ground black pepper.

Add the chicken to the hot pot in batches, skin side down, allowing space between each piece. Sear for several minutes per side, turning until the skin is deeply golden and crisped. Once browned, remove the chicken to a plate and set aside.

Pour off excess fat from the pan, leaving about a tablespoon to cook with. Add the quartered onions to the pot and sauté for about 5 minutes, stirring often until they soften and begin to release their natural sweetness.

Next, stir in the drained tomatoes, thyme, bay leaves, and a pinch of chile powder. Gently nestle the browned chicken pieces over the tomato mixture. Pour in the white wine and bring the pot to a light simmer. Cover with a lid and cook on medium-low heat for approximately 40 minutes, stirring occasionally to prevent the vegetables from sticking to the bottom.

Once the garlic has cooled enough to handle, squeeze the soft, roasted cloves into a small bowl. Mash the garlic into a smooth paste with a fork, season with salt and pepper, and reserve for serving.

After the chicken is fully cooked and tender, stir in the Dijon mustard until evenly combined. Raise the heat to medium-high and let the stew simmer uncovered for about 10 minutes. This final step thickens the sauce, allowing it to cling deliciously to each piece of chicken. Remove the bay leaves and adjust seasoning with additional salt and pepper if needed.

Serve hot over cooked rice or pasta, with a spoonful of the roasted garlic paste on the side for an added depth of flavor.