From The Food Network
Preheat the oven to 350 degrees F. Move one rack to the top of the oven.
In a saucepan, simmer the corn with the milk and onion powder, if using, for 5 minutes.
Combine the cornstarch with about 2 tablespoons water and stir well. Add the cornstarch to the corn mixture and whisk over medium heat for 3 minutes. Season the corn cream with a little nutmeg, salt, pepper and hot sauce if using. Remove from the heat, cover and keep warm.
Boil the elbow macaroni in full rolling salted water for 4 to 6 minutes. Drain the macaroni well and add to the corn cream. Add the Cheddar, half of the mozzarella and the egg. Stir well. Pour into a 4-cup casserole dish or 12-inch cast-iron skillet and top with the remaining mozzarella.
In a zip-top plastic bag, lightly crush the croutons using a small mallet or rolling pin. Stir together the oil and crushed croutons and spread over the top of the macaroni and corn mixture. Cook on the top rack until golden, 15 to 20 minutes. Serve with hot sauce.