Put the tomatoes into a pan with the chiles, cover with water, bring to a simmer, and cook at a fast simmer until fairly soft but not falling apart—about 5 minutes, depending on size of tomatoes. Set aside. Chop chiles roughly.

Put the garlic, chiles, and 1/3 cup (85 ml) of the cooking water into a blender jar and blend until well broken, about 5 seconds. Add the unpeeled, strained tomatoes and blend for a few seconds; the sauce should have a roughish texture. Heat the oil in a frying pan or cazuela, add the sauce, and cook over high heat, stirring from time to time and scraping the bottom of the dish, until reduced and the raw taste of garlic has disappeared-about 6 minutes. Add salt to taste.