There are some different ways to prepare this sauce:

1) In the blender: Tomato, onion, garlic, and chile, add little water to blend easier. This salsa doesn't need to be too smooth so you can use the lowest speed.

Fry the mix in a pot with one spoon of oil, when it starts boiling add salt and cumin. If your tomatillos are a little sour, you can add just a bit of baking soda. When it is ready remove from the pot and add the coriander finely chopped.

2) Boil the tomatillos and the chiles in water, when they are soft, put them in the blender with the onion, garlic, salt and cumin. Pour in a bowl, if the tomatillos are a little sour, add a bit of baking soda. Add the coriander finely chopped.

3) The same procedure as number 2, but the tomatillos and chiles instead of being boiled, must be grilled in a pan or comal. They have to be burnt outside and cooked inside, don't peel them, use them like they are and it will give a nice color and smoked taste to your sauce.

This sauce goes well with fried eggs, scrambled eggs, tacos, tostadas, quesadillas and grilled steaks.

Optional: When the sauce is not too warm you can add little pieces of avocado.

Note:
The reason why the coriander is not boiled with the tomatillos is because it will lose its beautiful green color, if you wash it well there won't be any problem to use it raw.