Preheat oven to 350 degrees F. Grease a 9x13-inch baking dish.
Cut 4 ounces of the Monterey Jack cheese into ½-inch cubes. Shred the remaining 4 ounces of Monterey Jack cheese; set aside.
In a large bowl, whisk together the flour, cornmeal, baking powder, salt, pepper and cayenne.
Place half of the corn and the scallion whites in the bowl of a food processor and pulse until it reaches a coarse puree, about 10 pulses.
Stir the pureed corn mixture into the flour mixture. Stir in the cubed Monterey Jack cheese, remaining half of the corn, sour cream, ¼ cup of the Parmesan cheese, eggs, and melted butter until combined. Transfer the mixture to the prepared baking dish and sprinkle with the shredded Monterey Jack cheese and remaining ¼ cup Parmesan cheese.
Bake until the casserole is slightly puffy and the cheese is golden brown, 45 to 50 minutes. Remove from the oven and let cool for 10 minutes. Sprinkle with the scallion greens and serve.