Rinse and stem the chiles, then place in a large pot. Add the tomatoes, onion, garlic, oregano, water and salt. Bring to a simmer, then
reduce heat to very, very low.
Simmer for 30 minutes. Place half of the solid ingredients in a
blender. Add about 1 cup of the liquid (do not use all of the liquid or the sauce will be too thin). Process until the ingredients are
pureed. Push the
puree through a fine sieve into a large saucepan. Use a spatula to scrape off all bits of
puree from the bottom of the sieve. Repeat with the remaining solids and 1 more cup or so of the liquid.
Simmer the sauce for about 10 minutes, tasting for seasoning. Add the half-and-half and continue to simmer for 5 minutes, until the sauce smooths out and the flavors come together.
