Remove husks from tomatillos and rinse off sticky film. Chop tomatillos and put into a sauté pan with high sides set to medium heat.

Add onion, garlic, lime juice, cumin, chili powder, and salt, and stir well to combine. Let mixture simmer for 15 minutes, until juices have released from tomatillos and they are softened.

Carefully pour salsa into a blender or food processor and pulse to chop. (Remember to vent at the top to release steam!)

Return salsa to sauté pan and stir in cilantro. Continue to simmer until thickened, then remove from heat.

Pour into reusable jars, and let cool before storing in the refrigerator.