Place the tomatillos and jalapeño on a jelly roll pan lined with foil. Place under the broil and broil until black spots appear (about 5-7 minutes). Flip and broil for an additional 5-7 minutes. Remove and let cool.

In a blender or food processor add the white onion through the salt along with the tomatillos and jalapeño. Blend until combined into a salsa mixture (do not fully close up the blender as the tomatillos and jalapeño are still warm. Keep the chute open and loosely place a towel over the opening). 

Taste and add any additional lime juice or salt. Refrigerate!