Preheat the oven to 350 degrees F. Lightly butter a deep 2 1/2-quart casserole.
Bring the large pot of salted water to a boil over high heat. Add the oil, then the elbow macaroni, and cook until the macaroni is just tender, about 7 minutes. Do not overcook. Drain well. Return to the cooking pot.
In a small saucepan, melt eight tablespoons of butter. Stir into the macaroni.
In a large bowl, mix the Muenster, mild and sharp Cheddar, and Monterey Jack cheeses.
To the macaroni, add the half-and-half cream, 1 and 1/2 cups of the shredded cheese from step #4, the cubed Velveeta, and the eggs (optional).
Season with salt and pepper.
Transfer to the buttered casserole.
Sprinkle with the remaining 1/2 cup of shredded cheese from step #4 and dot with the remaining one tablespoon of butter.
Bake until it’s bubbling around the edges, about 35 minutes. Serve hot.