Wash the tomatoes and remove the core/stem end with a sharp paring knife or tomato corer.

Trim the root end from the onions, remove any loose papery skin, and cut them into quarters through the root end.

Peel the garlic cloves and wrap them in a bundle of aluminum foil.

Get out the vinegar, cumin, oregano, and salt and measuring implements.

Place the cored Roma tomatoes, quartered onions, and bundle of garlic in foil on a half-sheet pan or several smaller baking pans (with a rim to collect the juices).

Roast the tomatoes and vegetables until they begin to brown, char, and soften.

Check the garlic after about 15-20 minutes, and remove the packet with tongs once it is soft and roasted (don't let it burn or it will be bitter).

Turn the tomatoes and onions over with tongs so that they cook evenly. The original recipe suggests 20 minutes, but I like to roast them a bit longer.

You can also grill the whole cored tomatoes for a smokier flavor.

Remove the sheet pan from the oven once the tomatoes are well roasted and the skins are loose. Let them cool until they can be safely handled.

While the vegetables are roasting in the oven, rinse the dried chiles with running water to remove any dirt, dust, or other field residue.

Shake off the excess water, then pat the chiles dry.

Heat a large cast iron or stainless skillet or griddle over medium to high heat.

Working in batches, toast and dry the washed chiles in the hot skillet until they are fragrant and puffed. Turn them with tongs to toast all sides. Don't let them char or burn or they'll get bitter.

Let the chiles cool slightly until they aren't too hot to handle.

Break off the stem end of the toasted chiles and shake out the dried seeds and loose membrane.

Tear the de-seeded chiles into a few pieces each, and place them in a large heat-resistant bowl.

Let the chiles soak until they are soft and re-hydrated, at least 15-20 minutes.

Peel the roasted tomatoes, and remove any tough outer skin layers from the roasted onions (save these for a roasted vegetable or meat stock).

Strain most of the soaking liquid from the dried chiles, reserving this in case you need to thin the salsa.

Blend together, working in batches, the re-hydrated chile peppers, tomatoes, onions, garlic, cumin, oregano, salt, and vinegar. You will need to do this in several batches, unless you have a giant commercial blender. Add a splash of chile liquid to each portion to make it easy to blend smoothly.

Pour the blended salsa into a large non-reactive pot, and use as much of the reserved chile soaking liquid as you need to get a thin, light-bodied salsa.

Stir everything together and check the consistency- this should be a light and relatively smooth salsa that will coat a spoon, not a thick chunky one.

Place the salsa pot on medium-high heat, stirring frequently.

Taste the tomato guajillo salsa and adjust the seasoning if needed (with more salt or vinegar, or canning-safe spices).

Bring the salsa mixture up to a full boil, and turn down or remove from the heat.

If you aren't canning your salsa, cool rapidly and portion into refrigerator or freezer-safe containers.

If you are canning it, keep the salsa hot until you fill the jars (have your jars and pre-heated water bath canner ready when the salsa is done, or keep the salsa hot on a very low heat until they're ready).

While you are roasting your vegetables and soaking your dried chiles, fill your water bath canner with water to a height that will cover your jars by several inches with room to boil vigorously.

Wash your jars and lids with hot soapy water, rinse, and place the jars (but not the lids) in the canner as you bring the water up to a low simmer or at least 180℉.

Protect your work surface- I like to use a baking sheet pan lined with an old kitchen towel, but you can also use a sturdy wire cooling rack or silicone mat. This helps protect the glass from temperature shocks and also makes for easier clean-up!

Remove your canning jars from the canner (carefully, with tongs or jar lifters, tilting them out of the hot water) just before filling and place them on the towel or rack.

Using a jar funnel if you have one, ladle the hot tomato guajillo salsa into the hot jars. Leave ¼” of headspace at the top of the jars (very slightly more if you are using reusable-style lids with gaskets like Weck or Tattler).

De-bubble the jars with a thin spatula, spoon, or de-bubbling tool, and wipe the tops of the jars with a clean paper towel or lint-free cloth that has been dipped in hot water or vinegar.

Place the canning lids on the clean jar tops and screw down the rings- don’t over-tighten the rings, just barely snug or “fingertip tight”. Regular canning lids are pretty forgiving but reusable lids need a more exact tension.

Using your jar lifter, tongs, or the canning jar rack, carefully place the hot filled jars of salsa in the preheated water-bath canner.

Make sure you have adequate water covering the jars (at least 2″ over the tops of the jars). Top up with water from a hot kettle if needed.

Start the timer for your water bath only after the water is at a rolling boil and all jars are in the canner. Process half-pint and smaller jars for 30 minutes (adjust for altitude if applicable, see recipe notes for chart) and then turn off the heat. There are no tested processing times for pint or quart jars of this salsa.

Leave the jars in the canner, and set another timer for 5 minutes.

Remove jars from the canner after the total time is up, and place them back on the towel-covered sheet pan or counter (put down a fresh towel if you spilled while filling the jars).

Leave jars of processed salsa to cool slowly in a draft-free place. Do not touch the lid rings until the jars are completely cool and sealed (if you are using reusable canning lids, follow manufacturer instructions). Do not stack jars while they are cooling (or in storage).