In a food processor or blender, blend the tomatillos, onion, jalapeno, garlic. Sauté the mixture in the olive oil for 5 minutes or until tender.
Blend the corn, and add with the stock, epazote, and some salt and pepper to the tomatillo mixture; heat until boiling.
Reduce the heat and simmer, covered, for 10 minutes.
Serve with fiesta chips, corn, crema, white queso fresco, topped with scallions.