In a medium saucepan combine the tomatillos, jalapenos, and garlic.
Add enough water to cover them and season with salt. Bring to a boil and then reduce to a simmer for 15 minutes.
Discard the water and transfer the rest to the blender. Blend until somewhat smooth but still with a bit of texture. Taste and adjust seasoning. Pour into a bowl and cover.
Refrigerate until cold. Add the cilantro and onions right before serving.