Preheat your oven to 400°F (200°C).

In a skillet over medium heat, add 2 tablespoons of olive oil. Once hot, add the sliced leeks and sauté until they are soft and beginning to caramelize, about 10 minutes. Season with salt and pepper. Remove from heat and set aside.

In a small bowl, combine the crushed allspice, salt, and pepper. Rub this mixture all over the beef tenderloin.

In the same skillet used for the leeks, add the remaining 2 tablespoons of olive oil and heat over medium-high. Sear the beef tenderloin on all sides until browned, about 2-3 minutes per side.

In a baking dish, place the seared tenderloin and surround it with the sautéed leeks.

Roast in the preheated oven for about 25-30 minutes, or until the beef reaches your desired doneness (135°F for medium-rare).

While the beef is roasting, prepare the garlic herb compound butter. In a medium bowl, combine the softened butter, minced garlic, fresh thyme, parsley, chives, and lemon juice. Mix well until all ingredients are incorporated. Transfer the mixture onto a piece of parchment paper, roll it into a log shape, and refrigerate until firm.

Once the beef tenderloin is done cooking, remove it from the oven and let it rest for 10 minutes before slicing.

Serve the sliced beef tenderloin with the roasted leeks and a dollop of garlic herb compound butter on top.