(Let your meat sit at room temperature for at least 30 minutes, until beef is no longer chilled.)
Preheat oven to 400F.
Season the meat with salt and pepper to your liking, on all sides.
Heat your skillet over medium high heat. Once hot, add butter. Once butter is melted, pan sear your filet mignon for 4 minutes each side. Add a little butter and swirl the juices around in the pan before you flip, and only flip once. Then transfer to the oven for additional cooking. About every 2 minutes will be an increment in the leve of doneness (again this is for an 8oz filet). 2 minutes in oven - medium rare 4 minutes in oven - medium 6 minutes in oven - medium well. Also, you can touch the filet to see how tough it feels (see details about the Finger Test).
Remove from oven and let it rest for at least 5 minutes (no poking, prodding or cutting!).
Reserve about 1 tablespoon of the drippings for the sauce, anything more keep for use in your yorkshire pudding.
Sauce: Heat the shallots in the skillet with the drippings for a few minutes until soft. Carefully add the broth and bourbon. Bring to a gentle boil, boil until reduced the liquid is reduced by half. Add cream and mustard, heat until the sauce has thickened. Remove from heat.
Recipe by Cake Student at https://www.cakestudent.com/filet-mignon-with-whiskey-sauce/