In a pot place 5 cups of water and set to boil. Add ¼ onion, 2 fresh garlic cloves, 7 tomatillos, and 1 serrano.
Cook the vegetables for around 7 to 10 minutes or until cooked.
Place the vegetables in the blender along with the 12 branches of fresh cilantro and ¼ teaspoon salt and ¼ teaspoon of the water where the vegetables are cooked.
Check if you would like more salt in this cooked salsa and add salt to taste.
Let the salsa cold down.
Now add the fresh ingredients, 1 tablespoon of chopped cilantro, 2 tablespoons of chopped onion, and the avocado chopped in small squares. It is important that the salsa is not hot when you add the fresh vegetables or they are going to cook in the salsa and these vegetables go fresh and add tons of flavor to the serrano pepper salsa.