Add the carrots, corn and broccoli to a large bowl. Add the coconut oil, season with salt and pepper and stir to coat the vegetables. Put the mixture on a baking sheet and roast until the broccoli tips are just browning and the corn is tender, 12 to 15 minutes. Set aside.
Meanwhile, bring a large pot of water to a boil and season generously with salt. Cook the macaroni as directed on the package and begin to make the cheese sauce.
Add the half-and-half, milk and both cheeses to a large saucepan set over medium heat and cook, stirring constantly to prevent sticking, until the cheese is melted and smooth and the sauce comes together. Season with 1/2 teaspoon pepper.
Drain the macaroni well, add to the cheese sauce and stir to combine. Add the roasted vegetables and stir again to cover with the cheese sauce. Drizzle with truffle oil before serving.