Season the beef medallions generously with salt and black pepper on both sides.
Use medium-high heat to heat olive oil and butter in frying pan until the butter has melted and starts to sizzle.
Add the seasoned beef medallions to the pan and cook for about 3-4 minutes per side for medium-rare doneness or adjust the cooking time to your preference.
Once cooked, transfer the medallions to a plate and cover with foil to keep them warm.
In the same pan, add the minced garlic and sauté for about 1 minute until fragrant.
Add Worcestershire sauce, Dijon mustard, beef broth, and heavy cream to the pan, whisking them together until well combined.
For 2-3 minutes allow the sauce to simmer until it gets some thickness.
Return the beef medallions to the pan and cook for an additional 1-2 minutes, coating them with the sauce.
Sprinkle chopped fresh parsley over the medallions and remove the pan from heat.