In a soup pot set over medium-high heat, melt the butter with the oil. Once it sizzles, add the onion and chile and cook for 3 to 4 minutes, until completely wilted and beginning to brown.
Add the corn and salt, stir, and cook for another 3 minutes. Add the epazote or cilantro and stir.
Pour in the chicken broth and bring to a simmer. Then cover, reduce the heat to low, and cook for 7 to 8 minutes. Turn off the heat.
Pour the soup into bowls and serve hot. Top with queso fresco.