Bring a large pot of salted water to a boil. Add the pasta and cook until just barely al dente (if you cook it until it's soft, gluten-free pasta will turn mushy). Drain well, transfer to a large bowl, drizzle with a bit of olive oil, and toss to combine. Set aside.

Heat a pot over medium heat, and melt the butter. Stir in the milk and whisk until bubbly. While whisking, add the cheese a bit at a time, and stir until completely melted. In a small bowl, combine the cornstarch and 2 tablespoons of water. Stir half of the cornstarch slurry into the cheese sauce, and see if it thickens up. If it doesn't, stir in the remaing cornstarch slurry. Season with salt and pepper, and fold in the pasta until well-coated. 

Serve hot.