Remove the beef tenderloin from the refrigerator and let it sit at room temperature for at least 1 hour to ensure even cooking. Preheat your oven to 475°F (245°C).

Halve the baby potatoes and arrange them in a large roasting pan around the beef once it’s ready. Drizzle olive oil and season with salt.

Melt the salted butter in a small saucepan, then mix in the Dijon mustard, Worcestershire sauce, chopped thyme, and garlic. Pour this mixture over the beef tenderloin.

Place the roast in the preheated oven and cook until the internal temperature reaches 115°F (46°C) for medium-rare, which typically takes about 25 to 40 minutes.

In a skillet, sauté the sliced cremini mushrooms in butter until golden brown. Add garlic and thyme, then pour in the Marsala wine and let it reduce. Stir in heavy cream and simmer until creamy.

Once your beef tenderloin reaches the desired temperature, remove it from the oven and allow it to rest for at least 10 minutes.

While the beef rests, smash the roasted baby potatoes, sprinkle with grated Parmesan, and return to the oven for about 10 minutes until crispy.

Slice the beef tenderloin and plate it with the creamy mushroom sauce and crispy smashed potatoes.