Grill the tomatillos and peppers over medium high heat, turning frequently until all the sides are blistered and partly blackened.
Remove the vegetables from the grill, place them in a large bowl, and cover it with a clean dish towel.
Put the onion, garlic, cilantro, lime juice, and salt into a food processor and pulse a few times.
When the grilled vegetables are cool enough to handle, cut the stems off them, cut in half, and either scrape out the seeds and membranes if you want a milder salsa verde or leave them in for a spicy salsa verde.
Add the tomatillos and peppers to the food processor and process until everything is smooth and evenly chopped.
This recipe freezes beautifully.
Feel free to mix and match different types of peppers to change the spiciness level. Poblanos and bell peppers are pretty mild while serranos and jalapeños are spicier.