Prepare the Roasted Leek Compound Butter: In a skillet over medium heat, add 1 tablespoon of olive oil. Add the chopped leeks and cook until they are soft and begin to caramelize, about 8-10 minutes. Remove from heat and let cool slightly. In a mixing bowl, combine softened butter, cooked leeks, thyme, parsley, lemon zest, and Dijon mustard. Mix until well combined and season with salt and pepper to taste. Transfer the compound butter onto a piece of parchment paper or plastic wrap, shape it into a log, and refrigerate until firm.

Prepare the Filet Mignon: Preheat your grill or a cast-iron skillet over medium-high heat. Pat the filet mignon steaks dry with paper towels and season generously with salt and freshly ground black pepper. In a small skillet, toast the coriander seeds over medium heat until fragrant, about 2-3 minutes. Remove from heat and let cool slightly, then crush the seeds slightly using a mortar and pestle or the bottom of a pan. Rub the crushed coriander seeds onto both sides of the filet mignon steaks.

Cook the Filet Mignon: Add the remaining tablespoon of olive oil to the hot skillet or grill. Place the steaks in the skillet and cook for about 4-5 minutes on each side for medium-rare, or until desired doneness is reached. In the last minute of cooking, add the chopped shallots to the skillet to char slightly.

Serve: Remove the steaks from the skillet and let them rest for about 5 minutes. Slice the chilled leek compound butter into rounds and place on top of the warm filet mignon. Serve the charred shallots alongside the steaks.