Preheat the oven to 325 degrees F. Lightly butter a 4-quart rectangular baking dish.
Bring a large saucepan of salted water to a boil. Add the macaroni and cook until slightly al dente, about 7 minutes. Drain and set aside to keep warm.
Whisk the eggs in a large bowl until frothy. Add the butter, Velveeta, and 1 cup of the half-and-half. Add the warm macaroni and toss until the Velveeta has melted and the mixture is smooth. Add the remaining 2 cups half-and-half, 1 1/2 cups of the yellow cheddar, the remaining cheeses, the salt, and the pepper. Toss until completely combined.
Pour the mixture into the prepared dish, and bake for 30 minutes. Sprinkle with the remaining 1 cup yellow cheddar and bake until golden brown on top, about 30 minutes. Serve hot.
Recipe courtesy of Delia Winder