Toast the chiles directly over a medium gas flame or in a cast-iron skillet until soft and brown, turning frequently to avoid scorching. Transfer the toasted chiles to a saucepan and add the vinegar and water. Bring to a boil, reduce to a simmer and cook 10 minutes to soften.
Transfer the chiles and liquid to a blender or food processor. Puree until a smooth paste is formed, adding a tablespoon or two of water if necessary to thin. Set aside.
Heat the olive oil in a medium saucepan over medium-high heat. Saute the onions until golden brown, 8 to 10 minutes. Stir in the garlic and cook briefly just to release the aroma. Then stir in the cumin and cook another minute. Add the chicken stock and reserved chile paste. Bring to a boil, reduce to a simmer and cook 20 minutes.
Meanwhile, mix together the brown sugar, orange and lemon juices, tomato paste, salt and pepper to form a paste. Add to the simmering stock mixture and continue cooking another 15 minutes. Adobo can be stored in the refrigerator 1 week or frozen indefinitely.
c.1997, M.S. Milliken & S. Feniger, all rights reserved