01 - Preheat your oven to 400°F (200°C). Lightly butter a medium-sized baking dish.
02 - Bring a large pot of generously salted water to a rolling boil. Cook the elbow macaroni until it is al dente, approximately 1 minute less than the package instructions suggest. Drain the pasta thoroughly and set it aside.
03 - In a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat. Add the all-purpose flour and whisk continuously for 1 minute to create a smooth roux.
04 - Gradually whisk in the whole milk into the roux, ensuring there are no lumps. Continue to cook and stir constantly until the sauce thickens to a smooth consistency, which should take about 4-5 minutes.
05 - Remove the saucepan from the heat. Stir in the grated Gruyère, white cheddar, and Parmigiano-Reggiano cheeses. Add 1 teaspoon of truffle salt, freshly ground black pepper, and nutmeg (if using). Continue to stir until the cheese is completely melted and the sauce is smooth and homogenous.
06 - Gently fold the drained macaroni into the cheese sauce. Add 1 tablespoon of truffle oil and mix thoroughly to ensure all the pasta is evenly coated.
07 - Transfer the macaroni and cheese mixture into the prepared baking dish. Drizzle the remaining 1 tablespoon of truffle oil over the top and gently swirl it into the surface.
08 - In a small separate bowl, combine the panko breadcrumbs, melted butter, and 1/4 teaspoon of truffle salt. Mix until the breadcrumbs are evenly moistened. Sprinkle this mixture uniformly over the macaroni and cheese.
09 - Place the baking dish in the preheated oven and bake for 15-18 minutes, or until the topping is golden brown and the macaroni and cheese is bubbling.
10 - Carefully remove the dish from the oven. While the macaroni and cheese is still hot, thinly shave the fresh black truffle over the top. If desired, garnish with fresh chopped parsley.
11 - Serve the Truffle Mac Attack immediately to best appreciate the intense truffle aroma and flavor.