Preheat oven to 325 degree. lightly butter a 4 quart baking dish. Bring a large saucepan of salted water to a boil. add the macaroni and cook until slightly al dente, about 7 min. Drain and set aside
Whisk the eggs in a large bowl until fluffly. add butter, velveeta and 1 cup of the half-half. add the warm macaroni and toss until the velveeta has melted and the mixture is smooth. add the remaining 2 cups half-half, 1 1/2 cups of the yellow cheddae, the remaining chesses, the salt, and the pepper. toss until completely combines.
Pour the mixture into the prepared dish, and bake for 30 minutes. Sprinkle with remaining 1 cup yellow cheddar can bake until golden brown on top.about 30 minutes.Serve Hot.