01 -
Break guajillo chiles into pieces and remove seeds. Add them with the chiles de árbol to a dry skillet over medium heat. Toast 20-30 seconds per side until darkened and fragrant. Remove immediately before they burn.
02 -
Transfer toasted chiles to a bowl and cover with hot water. Soak for 15 minutes until completely soft. Drain and discard the soaking liquid.
03 -
Combine tomatoes, onion, and garlic in a small pot. Cover with water, bring to a boil, and simmer 10 minutes until the tomato skins split and the flesh is fully soft. Drain.
04 -
Add drained tomatoes, onion, garlic, soaked chiles, cumin, and 1/3 cup fresh water to a blender. Blend on high until completely smooth. Add more water a tablespoon at a time if needed for a pourable consistency.
05 -
Heat oil in a medium saucepan over medium-high until shimmering. Pour in the blended salsa carefully (it will splatter). Cook uncovered, stirring occasionally, for 8-10 minutes until the color deepens and the salsa thickens slightly.
06 -
Remove from heat. Season generously with salt. Stir in cilantro if using. Cool completely before transferring to a sealed glass jar.