Boil the pasta in a large pot of water until al dente. Drain and set aside. Preheat oven to 350. Butter a baking dish. In a saucepan over medium heat, add the butter and flour and cook for one minute. Add the milk and cream and whisk until it starts to thicken. Add the truffle oil and truffle salt and stir. Add in 3 cups of the cheese and mix until the cheese is melted. Add the pasta to a mixing bowl. Pour the cheese sauce on top and mix until all of the pasta has the cheese sauce on it. Pour it into the buttered dish. Top with 1/2 cup of gruyere cheese. Combine ingredients for the topping and sprinkle on top of macaroni and cheese. Bake for 20-25 minutes or until it starts to bubble and the breadcrumbs start to brown. Remove from oven and serve.
