How to Make It
In a large saucepan, bring the water to a boil. Add the chiles and simmer over moderately high heat, stirring occasionally, until tender, about 8 minutes. Drain the chiles, reserving 3 cups of the cooking water. Transfer the chiles and reserved cooking water to a blender and let cool slightly; puree until smooth.
Wipe out the saucepan. Add the bacon and cook over moderate heat, stirring occasionally, until it just starts to render, about 5 minutes. Add the onion, garlic and oregano and cook, stirring occasionally, until softened, about 7 minutes. Stir in the flour and cook, stirring, until the pan is dry, about 2 minutes. Stir in the chile puree and bring to a simmer. Cook over moderate heat, stirring constantly, until the sauce is thickened and the flavors meld, about 12 minutes. Press the mixture through a fine sieve into a heatproof bowl; discard the solids. Stir in the sugar and season with salt. Use immediately or let cool completely.