Preheat oven to 400°F.
Roast garlic for 20 minutes and onion for 35 minutes or until softened. Peel and reserve in a medium bowl to catch any juices.
Place tomatillos in medium saucepan, add salt and water to cover and bring to a boil over high heat. Reduce heat and simmer for 3 minutes. Drain and add to garlic and onion.
Heat the vegetable oil over medium high heat until hot but not smoking. Add pumpkin seeds and sauté, shaking the pan constantly for approximately 4 to 5 minutes. Do not let the seeds burn or they will turn the whole sauce bitter. Reserve ¼ cup for garnish.
Place the pumpkin seeds in the container of the blender with the garlic, onion, tomatillos, and all the remaining ingredients and process until smooth, about 2 to 3 minutes. (A food processor does not work well in this recipe.) Pour sauce into a large saucepan and simmer gently over low heat, stirring often, for 10 minutes.