Toast the torn ancho and guajillo chiles in a dry skillet over medium heat, stirring often, for 1 to 2 minutes until fragrant. Stop the moment they smell toasty; scorching them makes the sauce permanently bitter.
Transfer the chiles to a pot, add the bay leaf, and cover completely with water. Bring to a boil, remove from the heat, cover, and soak 10 minutes until soft.
Lift the softened chiles and bay leaf into a blender with a slotted spoon. Add 3 cups of the soaking water, the garlic, vinegar, soy sauce, oregano, thyme, sugar, cumin, and salt. Blend smooth and set aside. (For deeper, less astringent sauce, simmer the raisins with the chiles and add the orange juice concentrate to the blender now.)
Heat 1 tablespoon oil in a Dutch oven over medium-high. Sear half the pork on all sides until browned, then move it to a plate.
Add 1 tablespoon oil and sear the remaining pork the same way; set it with the first batch.
Add the last 1 tablespoon oil and the onion. Cook about 5 minutes, scraping up the browned bits stuck to the bottom.
Return all the pork to the pot and pour the blended chile sauce over it. Stir to coat.
Bring to a boil, reduce the heat to low, cover, and braise 2 hours, until the pork is fork-tender. Do not push past done. Serve with cilantro, lime, and warm tortillas.