How to Make It
Rinse the chilpotles and drain. Pierce each one all the way through with a sharp fork or skewer. Place in a pressure cooker with water to cover and cook at low pressure for about 15 minutes; they should be soft but not mushy. (Alternatively, cook the chiles with water to cover in a tightly covered nonreactive medium saucepan over low heat for 30 to 40 minutes.)
Drain the chilpotles, remove the stems and wipe off any stray seeds clinging to the outside. Set aside.
Meanwhile, in a medium nonreactive saucepan, cover the anchos with hot water and simmer for 5 minutes. Drain and transfer to a blender. Add 1 cup of water plus the garlic, marjoram, thyme, cumin seeds, bay leaf and 4 of the cooked chilpotles and blend until almost smooth.
Heat the oil in a shallow nonreactive skillet. Add the blended ingredients and fry over moderately high heat for about 3 minutes, scraping the bottom of the pan to prevent sticking. Add the vinegars, brown sugar, salt and 1/2 cup of water and cook for 5 minutes longer. Then add the remaining chilpotles and cook over moderate heat, scraping the bottom of the pan from time to time to prevent sticking, until the sauce has reduced and thickened, about 15 minutes.