Wash the tomatillos with warm water to remove the husks and sap.
Roast the tomatillos over hot coals until charred. Do not brush the tomatillos with oil, instead let them char and blacken on the outside (10-15 minutes). Place them in a bowl to cool.
Roast the serranos and jalapeños aiming for a good char all over the peppers. Do not remove the skin.
Add the tomatillos and any liquid that has rendered to the canister of a blender. Pulse until the tomatillos are chopped.
Wearing gloves, remove the seeds and pith of the chiles if you prefer less heat. Keep them whole if you prefer more. Start with 1 Serrano and 1 jalapeño and add more another, if necessary. Cut off the stems of the chiles and add them to the blender with the tomatillos. Pulse until blended.
Next, add 2 cloves of garlic and pulse.
Add the lime juice and pulse.
Add the Green Chile Rub and pulse. Pour the salsa into a bowl and stir in the finely chopped red onion.
It is ready to serve, but for the best flavor, refrigerate overnight. It will last a week in the fridge.