Step 1 If using prunes with pits, bring one cup of water to a boil and pour the boiling water over the prunes to soften, about 15 minutes; drain and use a scissors to pit them. Quarter the prunes.
Step 2 Quarter the kumquats lengthwise, remove the seed and center pith, and if you feel energetic, cut the quarters in half again lengthwise. Set the prunes and kumquats aside.
Step 3In a wide pot, heat the oil over medium heat. Working in batches if necessary to avoid crowding, add the chicken, season generously with salt and pepper, and brown, turning as needed, until golden on all sides, 10 to 12 minutes. Remove the chicken to a plate.
Step 4Pour off all but 1 to 2 tablespoons of the fat from the pot, reduce the heat to medium-low, and add the onion. Stir well, scraping the pan bottom to loosen the brown bits, and cook, stirring occasionally, until the onion is translucent and soft, 5 to 7 minutes.
Step 5Add the garlic, stir and cook for 1 minute more. Add the wine, raise the heat to medium, and cook, stirring to deglaze the pot, until the liquid is reduced by slightly more than half, about 3 minutes.
Step 6Return the chicken to the pot and add the prunes, kumquats, olives, and a little salt and pepper. Stir, cover, reduce the heat to low, and simmer for 20 minutes. Adjust seasoning as necessary. Add one-fourth cup of the stock, and simmer covered until the chicken is very tender, about 1 hour, basting occasionally with the sauce and adding stock, if needed, to keep the chicken half-submerged in the sauce. The dish may be made a day ahead and reheated. Serve with couscous or rice. To serve with harissa, remove a little of the sauce from the chicken and stir in harissa to taste; drizzle over plated dish.