Some serranos are fiery hot while others have a mild, almost grassy taste, so boil a few, then taste a small piece of each to decide how much you want to add to your salsa.
In a medium saucepan over medium-high heat, add tomatillos, serrano chilies, onion, and garlic, and enough cold water to cover. Bring to a boil, reduce heat, and simmer until tender and cooked through, about 20 to 25 minutes.
Using a slotted spoon, transfer to a molcajete or blender and grind or process until smooth. Season to taste with salt (I like 1/2 teaspoon) and cool.
Notes
Tomatillos: Tomatillos look like unripe green tomatoes wrapped in a papery husk. After you remove the husk, the tomatillos might feel sticky underneath. Just rinse them off and you’re good to go. These become very soft and will burst in the water as they boil, so always boil the ingredients for the two salsas separately.
Serrano chilies: Boil all 3 chilies, then taste a small piece of each to determine how spicy they are and how much you want to add. Some serranos are fiery hot while others have a mild, almost grassy taste.
Yield: This recipe makes about 2 cups of salsa, enough for 8 servings, 1/4 cup each.
Storage: Store leftover Salsa Verde covered in the refrigerator for up to 4 days.