Place 2 of the prunes in a bowl and pour on boiling water to cover. Let sit 15 minutes, and drain.

Roast the onion and tomatoes. Cover a baking sheet with foil and preheat the broiler. Place the tomatoes and onion on it (you may have to do this in batches) and set under the broiler, about 2 to 3 inches from the heat. Turn after 2 or 3 minutes, or when the tomatoes have charred on one side, and repeat on the other side. As the tomatoes are done, transfer them, using tongs, to a large bowl. The onion will take longer than the tomatoes and will have to be flipped over several times so that it doesn’t char to a cinder. It should be charred and softened in 5 to 10 minutes. Transfer to the bowl with the tomatoes. When the tomatoes are cool enough to handle, core and peel.

Toast the garlic in its skin in a dry skillet or on a griddle over medium-high heat. Turn the cloves often, until they are blackened in a few spots and smell toasty, about 10 minutes. Remove from the heat and peel.

Grind the pepper and clove in a spice mill. Transfer the tomatoes, along with any juices from the bowl, the roasted onion, the garlic, ground pepper and clove, the two soaked prunes, and the chipotles to a blender. Blend until smooth, and pour into a bowl through a medium strainer lined with cheesecloth. Tap the strainer against the bowl to get all of the puree through.

Heat 2 tablespoons of the oil over medium-high heat in a large, heavy nonstick skillet and brown the chicken on both sides until golden, about 5 minutes per side. Season each side after you flip the chicken over. Transfer to a plate or bowl as the chicken is done. When all of the chicken as been browned, pour off the fat from the pan.

Heat the remaining oil in the pan over medium-high heat, and add a drop of the pureed tomato mixture. If it sizzles loudly, add the rest (wait a minute or two if it doesn’t). Add the puree and cook, stirring, until it thickens slightly, about 5 minutes. Stir in 1/2 cup chicken stock or water and 1/2 teaspoon salt. Bring to a simmer, turn heat to low and simmer uncovered for 20 minutes, stirring often, until the sauce is fragrant and thick. Add the chicken pieces, the remaining prunes, the cinnamon, the remaining stock or water, and salt, bring to a simmer, reduce the heat, and simmer 30 to 40 minutes, until the chicken is tender. Taste and adjust seasonings. Serve hot, with rice.

Keeping time / Leftovers
The dish will keep for 3 or 4 days in the refrigerator. Shred leftover chicken and serve with rice, or make tacos or enchiladas with the leftover chicken and sauce.