In a skillet heat oil and brown mushrooms 10 minutes. Scrape corn from cobs and add to mushrooms, season with salt and pepper and cook 5 to 6 minutes more. Reserve.
In a blender or food processor combine peppers with stock, onions, garlic, cilantro, salt and pepper, puree. In a saucepot over medium heat melt butter, whisk in flour, add milk and cream and raise heat a bit, add Poblano puree and simmer to thicken and cook sauce, 20 to 25 minutes, stir in 1 cup of grated cheese.