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.
Bring large pot of water to boil, salt it and cook pasta to al dente, reserve a ladle of starchy cooking water. Drain pasta and toss with sauce, mushrooms and corn, add a little starchy water if too thick. Place in individual serving dishes and top with remaining Manchego. Cool and store for make-ahead meal. Bake from room temperature at 350F to brown and bubbly, 15 to 20 minutes if freshly prepared- 30 to 40 minutes if from room temp after being refrigerated.