1 pound tomatillos
4 scallions
2 to 4 serrano chiles
1 teaspoon Mexican lime juice
1/2 teaspoon salt, or to taste
1/2 teaspoon granulated sugar (optional)
1/3 cup cilantro (optional)

NOTE: Do not add cilantro if the sauce is going to be used as an enchilada sauce.

Place the tomatillos and chiles in a pot and cover with water. Bring water to boil over medium heat. If you use high heat, the tomatillos can easily disintegrate if the water is allowed to boil too swiftly. When the tomatillos and chiles have become quite soft, about 5 to 10 minutes, discard the water and place them in a blender. Add onions, lime juice and salt; blend, using pulses, until the sauce is roughly chopped. Taste the sauce and add the sugar, if necessary, and the cilantro, if desired. If the sauce is to be used in enchiladas, blend it for about 15 seconds or until it is smooth.