Prepare the Potatoes: Place the cubed potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil. Cook the potatoes for about 15-20 minutes, or until fork-tender. Drain and return to the pot. Add heavy cream, truffle oil, and grated Parmesan cheese to the potatoes. Mash until smooth and creamy. Season with salt and pepper to taste. Keep warm.

Roast the Asparagus: Preheat your oven to 400°F (200°C). Place the trimmed asparagus on a baking sheet. Drizzle with olive oil, lemon juice, and season with salt and pepper. Toss to coat. Roast in the oven for 12-15 minutes, until tender and slightly crispy.

Cook the Filet Mignon: While the asparagus is roasting, heat olive oil in a large skillet over medium-high heat. Season the filet mignon steaks with salt and pepper on both sides. Add the steaks to the skillet and cook for 4-5 minutes on each side for medium-rare, or until your desired doneness is reached. In the last minute of cooking, add butter and minced garlic to the skillet. Spoon the melted butter over the steaks for extra flavor.

Serve: Plate the creamy truffle mashed potatoes, top with the filet mignon, and arrange the roasted asparagus on the side. Garnish with fresh parsley before serving.