This makes alot but freeze it smaller serving batches
6 ½ pounds/about 100 ounces canned whole, peeled plum tomatoes and their juices (or one restaurant-style No. 10 can or 4 28 oz cans)
1 bunch cilantro, leaves and stems washed and roughly chopped
1 cup peeled garlic cloves
4 serrano chiles, stems and seeds removed then roughly chopped
2 guajillo chiles, stems detached
1 tablespoon achiote paste
Kosher salt, to taste
Optional mexican oregano to taste
Combine everything in a large pot or rondeau, and simmer over gentle heat for 1 hour, stirring occasionally to prevent any scorching on the bottom. Add a little water if it becomes any thicker than ketchup. Allow to cool before puréeing.
Working in a blender in batches, purée until smooth. Check the salt seasoning. Let cool.
Transfer to quart or pint containers, and stock your freezer, or put the sauce in something more attractive — rubber-sealed jars with hinged lids? — to make gifts of the stuff. Ranchero sauce keeps well in the refrigerator for up to 2 weeks, or in the freezer for up to 1 year. (It may separate a little, in which case you can simply reheat and give a new buzz in a blender to reunify.)