2While the chiles rehydrate, peel the Garlic cloves and roughly chop the White onion. Toast the Cumin seeds lightly in a dry pan until fragrant, then grind them if using whole.
3Drain the rehydrated Guajillo chiles and Ancho chiles, reserving a small amount of the soaking liquid. In a blender, combine the softened chiles, Achiote paste, Garlic cloves, White onion, ground Cumin seeds, Mexican oregano, Lime juice, Orange juice, Sea salt, and Black pepper. Add a splash of the reserved chile soaking liquid if needed to achieve a smooth, thick marinade. Blend until completely smooth.