Cook the onions in the butter until clear. Add the garlic, cilantro (reserve a couple of spoonfuls for garnish), cumin, and oregano and let cook for another 2 minutes. Add the meat of 5 avocados, lime juice, Crema Mexicana, and chicken s tock. Slowly bring to a boil. Lower flame and simmer for 15 minutes. Let cool c ompletely before pureeing in a blender. Check for salt and pepper and lime. Ser ve with cubes of avocado, the remainder of the chopped cilantro and sprinkle wi th Cotija cheese.