Prepare the Compound Butter: In a skillet over medium heat, add a small amount of olive oil. Add the finely chopped leek and sauté until softened and fragrant, about 3-4 minutes. Remove from heat and let cool.

In a mixing bowl, combine the softened butter, sautéed leek, smoked paprika, and a pinch of salt. Mix until well combined.

Transfer the mixture onto a sheet of plastic wrap. Roll it into a log shape, twisting the ends to seal. Refrigerate until firm, about 1 hour.

Prepare the Beef Tenderloin: Preheat your oven to 400°F (200°C).

In a small dry skillet, toast the mustard seeds over medium heat until they begin to pop and become fragrant, about 2-3 minutes. Remove from heat and let cool.

In a bowl, combine the toasted mustard seeds, wild thyme, olive oil, salt, and pepper. Mix until well combined.

Rub the beef tenderloin all over with the mustard seed mixture, ensuring it is evenly coated.

Sear the Beef: In an oven-safe skillet, heat a tablespoon of olive oil over medium-high heat. Add the beef tenderloin and sear on all sides until browned, about 2-3 minutes per side.

Roast the Beef: Transfer the skillet to the preheated oven and roast the beef for about 20-25 minutes, or until the internal temperature reaches 130°F (54°C) for medium-rare. Remove the skillet from the oven and let the beef rest for 10 minutes before slicing.

Serve: Slice the beef tenderloin into medallions and serve with slices of the smoked leek compound butter on top. Garnish with freshly chopped chives.