One-three serranos depending on their heat and your tolerance for it. I like to put them in a pan w/ olive oil and slowly fry them until they get a little blackened, but fresh chopped works great also.
About one half dozen tomatillos
broil and peel off the skin, also do this if you use tomatoes.
Garlic- 2-4 cloves, your preference. Heat on hot cast iron skillet until the skin blackens, cool and peel.
About 3/4 to one whole white onion diced
A handful of chopped cilantro
salt and lime to taste.
I like mashing the ingredients in a big stone mortar and pestle I got in Mexico. It's rustic and has creates great texture in the salsa. You can use the blender, but just pulse the blender to get the desired texture. You don't want it pureed.
This is a terrific salsa and very authentic. You can substitute jalapenos for serranos, also.