Pre-heat oven to 250.
Bring steaks to room temperature, about 20 minutes before cooking.
Heat skillet on medium-high heat, until very hot.
Season steaks on both sides with salt. Press into the peppercorns. Let steaks sit 10 minutes. This allows for the pepper to adhere and flavor the steak.
Heat olive oil in the skillet and place the steaks pepper side down. Cook 3 minutes, turn, and toss 1 Tbsp butter into the skillet. Baste the steaks with the butter, and cook 2 minutes more.
Remove the filets to a plate, cover tightly with foil, and place into the oven to keep warm.
Meanwhile, turn the heat on the skillet down to medium. Make the pan sauce by adding 1 Tbsp olive oil in the skillet over medium heat. Sauté the mushrooms, about 4 minutes. Stir, then remove the pan away from the flame.
BE VERY CAREFUL: Have a large lid handy in case things get out of hand (they shouldn't but be prepared). With the skillet away from the flame, add the brandy, then return the skillet to the flame. The brandy may catch fire, but it shouldn't burn for more than 10 - 15 seconds. Allow the alcohol to burn off.
Add the stock and bring to a low boil to reduce a bit, about 5 minutes.
Toss the butter into the skillet. Season the sauce with salt and pepper to taste.
Plate the filet, and spoon the sauce over the top.