Rub the beef filets with olive oil, salt, and black pepper.
Heat a skillet over medium-high heat and sear the filets for 3-4 minutes on each side.
Remove the filets from the skillet, cover them with foil, and keep warm.
In the same skillet, add butter and sauté the mushrooms for 5 minutes.
Stir in the garlic and cook for 1 more minute.
Add the beef stock and cream to the skillet, bringing it to a simmer.
Stir in thyme, salt, and black pepper, and cook for 2-3 minutes until the sauce thickens.
Return the beef filets to the skillet, coat them with the sauce, and cook for an additional 1-2 minutes.
Serve hot.