Roast the tomatoes and tomatillos until charred on all sides, about 10-12 minutes.
Place the tomatoes, tomatillos, water, chiles de arbol and onion into a sauce pan, bring to a boil and simmer until the onions are tender, about 20-30 minutes.
Drain the water reserving it.
Place everything other that the sesame seeds into a food processor or a blender and puree adding some of the reserved liquid if necessary.
Strain the bits from the salsa.
Mix in the toasted and crushed sesame seeds and season with salt and pepper.
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