Start by bringing your filet mignons to room temperature. Season both sides generously with coarse salt and fresh cracked pepper.
Place your cast iron skillet on the stovetop over high heat. Allow it to preheat for about 5 minutes.
Once the skillet is hot, add 4 teaspoons of olive oil. Swirl it around to coat the bottom of the skillet.
Carefully place the seasoned filet mignons in the skillet. Sear each side for 2-3 minutes until a deep brown crust forms.
After flipping the steaks, add the slices of ice-cold butter to the pan. Spoon the butter over the steaks to baste them.
Use a meat thermometer to check the internal temperature. Aim for about 125°F (51°C) for rare.
Once cooked, remove the steaks from the skillet and place them on a cutting board. Cover loosely with aluminum foil and let them rest for about 5 minutes.
Slice the steaks against the grain and serve immediately. Drizzle any leftover pan juices over the top.