Add tomatillos and serrano peppers to a large pot. Pour in enough chicken stock to cover tomatillos. Simmer until tomatillos are soft (approximately 15-20 minutes).
Toward the end of the cooking time, add olive oil to a large skillet. Add onions and saute until onions are translucent. Add in the minced garlic toward the end and heat until fragrant. Set aside until.
Pour tomatillos in a blender or food processor. Add in half a bunch of cilantro and puree for 15-20 seconds.
Pour tomatillo mixture into the pan with the onions and garlic and simmer for about 8 minutes.
Add in the salt, pepper, cumin, ground garlic and white pepper. Let that saute for a few minutes.
Add in vinegar and sugar and let the mixture to continue to simmer for 5 more minutes. Add additional chicken stock to the mixture anywhere along the process if the sauce gets too thick.
Once the sauce has cooked down a bit, taste and determine if more salt is needed. Season to taste.
The salsa verde can be used over white cheese or chicken enchiladas