Slice the beef tenderloin steaks in half or thirds to make medallions.
Pat dry the beef tenderloin medallions with a paper towel, then season with sea salt and black pepper
Dredge the filet pieces in all-purpose flour.
Melt the butter in a large saute pan over medium-high heat.
Add the beef and saute for about one minute on the first side, then turn over the beef and saute on the other side for about one minute.
Remove the beef from the pan, place it on a plate, and cover it loosely with aluminum foil to keep it warm.
Add the mushrooms, shallots, and garlic to the pan.
Saute, stirring often, until the mushrooms are soft (about 2 minutes).
Remove the pan from the heat and add the Jack Daniels.
Light the alcohol with a grill lighter or simply saute for a minute to allow the alcohol to burn off.
Add the Dijon mustard and heavy cream, mix thoroughly, and cook the creamy sauce, stirring, for about 1 minute.
Add the beef stock to the sauce and simmer for 1 minute. Add the Worcestershire and stir to combine.
Place the pieces of butter in the flour and push the flour into the butter. This is called a beurre manie (butter and flour).
Add the beurre manie to the pan to thicken the sauce.
Return the meat and any accumulated juices to the pan and turn the meat to coat with the sauce.
The steaks will be medium to medium rare. For more well-done, cook the medallions a little longer. For a precise internal temperature, use an instant-read thermometer or meat thermometer to check the internal tempe
Divide the medallions between two plates and top with sliced green onions and chopped fresh parsley.