In a shallow bowl, toss the onion slices with the turmeric and salt. Cover the onion with plastic wrap and let stand overnight at room temperature.
Meanwhile, heat a cast-iron skillet until hot to the touch. Add the anchos and chipotles and toast over moderate heat, pressing lightly with a spatula until the chiles are very pliable and fragrant, about 1 minute. Transfer the chiles to a work surface and let cool completely, then tear them into 1-inch pieces. In a spice grinder, coarsely grind the chiles.
Drain the onion slices in a strainer, pressing hard to extract as much liquid as possible. Transfer the onions to a food processor and pulse until pureed. Add the ground chiles, coriander, caraway, pepper and cinnamon and process to a paste. With the machine on, gradually add the olive oil and puree until fairly smooth.
The harous can be refrigerated for up to 6 months.