everything out and to start making a sauce. Add a big pinch of salt.
In a separate pan, heat another splash of oil over medium-high
heat. When it’s nice and hot, add the onions and cook quickly to
caramelize them* to a light golden color. Add the onions to the
blender along with the garlic. Place the cinnamon stick, black
peppercorns, and oregano in the cast-iron skillet in which you
toasted the garlic and heat them until fragrant, 2 minutes or so; add
them to the blender. Add about 1 cup chicken stock and blend
until you get a smooth puree.
Strain the puree into the guajillo chili sauce and stir, tasting and
adjusting the salt. Allow this to simmer for 30 minutes over low
heat, during which time the flavor will continue to develop.
When the sauce is ready, cook the steaks. Remove the steaks
from the plastic bag, scraping off most of the marinade (no need to
be meticulous about this), and heat a cast-iron skillet over very
high heat. Sprinkle the steaks with a little more salt and add a
splash of vegetable oil to the skillet. Sear the steaks, two at a time,
on both sides until crusty and cooked to your preference (about a
minute on each side for medium rare*). Serve immediately with a
big ladleful of the warm guajillo chili sauce on top.
* This isn’t a slow caramelization like you’d do for French onion
soup; it’s a fast caramelization.* Because flank steaks are so thin, you can’t really tell by
touching if they’re cooked properly. The best way to know for
sure is just to cut right into the middle of a piece while it’s still