Grab a small bowl. Combine the Dijon mustard, balsamic vinegar, olive oil, sea salt, and cracked black pepper. Whisk this mixture until it's fully blended.

Next, take that beautiful beef tenderloin and place it in a shallow dish. Pour your marinade over the meat, making sure every inch is well-coated. Remember, this is where the flavor starts! Cover the dish and let it marinate in the refrigerator for at least one hour. If you're feeling bold, let it sit longer—up to four hours will deepen the flavor.

While the beef lounges in that marinade, heat your grill or preheat your oven to 425°F. If you’re grilling, oil the grates; if you’re roasting, a baking sheet will do just fine.

Take the beef out of the fridge and let it sit at room temperature for about 15—20 minutes. This step ensures even cooking.

If using a grill, place the tenderloin directly onto the grates. Sear it for about 5 minutes on each side. If you’ve opted for the oven, place it in the preheated oven and roast for about 25-30 minutes to reach medium rare. Remember to use a meat thermometer—130°F is your target for that perfect juicy tenderness.

Once it reaches that glorious temperature, remove it from the grill or oven. Tent it loosely with foil and let it rest for at least 15 minutes. This trick allows juices to redistribute, ensuring that every bite is flavorful.

Slice the tenderloin against the grain into thick medallions. Serve it with a dollop of Basil Parmesan Mayonnaise. This tangy, creamy topping perfectly complements the rich beef, making it a match made in culinary heaven.