Coarsely chop the onions, tomatoes, tomatillos, and serrano chiles.
Add the garlic to the molcajete and grind to a paste.
Add the onion and grind until it starts to break apart.
Add the cilantro.
Add the Roma tomatoes and tomatillos and grind until desired consistency is reached.
Salt to taste.
Notes
Where to Get a MolcajeteYou can get a molcajete through HERNÁN, specialists in authentic Mexican foods and cookware.Substitutions
You can substitute jalapeños for the serrano chiles. You can make the salsa with just Roma tomatoes or just tomatillos.
Preparation
If you prefer a less chunky salsa, chop the ingredients finer before grinding them in the molcajete.
Really charring the ingredients adds lots of flavor to the salsa.
You do not need to remove the seeds and veins from the chiles.
Be sure to add enough salt to the salsa so that all of the flavors really pop. The salsa should be a little bit salty when you taste it on its own. When you add it to your food it won't taste as salty.
You can also make this salsa in the blender. It will still taste great.
Storage
It keeps well in the refrigerator for up to 3 days.
What the Name MeansThe name "salsa molcajeteada" means salsa made in a molcajete.