Set the beef tenderloin on the kitchen counter for 1 hour before cooking to come to room temperature.
Preheat oven to 450˚F.
Pat dry the beef with paper towels.
In a small mixing bowl, combine salt, pepper, thyme, oregano, and olive oil; mix to combine. Rub the mixture on the beef tenderloin.
Tie with twine: Place the tenderloin over pieces of precut kitchen twine spaced one inch apart and tie them closed. You can also ask the butcher to do this for you.
Optional but Recommended: Heat 1 tablespoon of vegetable oil in a large skillet. Add the beef tenderloin to the hot oil and sear on all sides until browned—about 2 to 3 minutes per side.
Place beef on a jelly roll pan, tucking the thin end under the meat if it is not already tucked underneath and tied.
Roast for 25 to 30 minutes, or until internal temperature registers at 130˚F to 135˚F. Cooking time may vary depending on the size of the tenderloin; use an instant read thermometer to check for doneness. Start checking around the 22-minute mark.
Remove from oven and transfer beef to a cutting board. Tent a piece of foil over the beef and let rest for 10 to 15 minutes before cutting.
For The Gravy
In the meantime, prepare the gravy and set a large skillet over medium-high heat, and melt the butter. Add garlic; cook for 10 seconds or until fragrant.
Stir in the mushrooms; season with salt and pepper and cook for 5 minutes, undisturbed.
Stir and continue to cook the mushrooms for 3 to 4 more minutes or until very tender and caramelized.
Remove mushrooms from skillet and set aside; keep covered.
Set the skillet back over medium-high heat. Add wine or broth to the hot skillet and scrape up any browned bits from the bottom of the pan. Continue to simmer for 3 to 4 minutes or until the liquid has reduced by a third.
Slowly pour in the cream while whisking. Then, whisk in the dijon mustard. Whisk until everything is well incorporated.
Bring mixture to a boil; then, reduce heat to medium-low and simmer 5 to 7 minutes, or until sauce has started to thicken. IF your gravy hasn't started to thicken, turn off the heat and stir in a tablespoon of butter until completely combined and mixture is thickened. Gravy will continue to thicken as it cools.
Remove the skillet from heat. Gently stir mushrooms back into the gravy.
Taste for salt and pepper and adjust accordingly.
Cut the beef tenderloin into ¼-inch slices and serve with prepared mushroom gravy.
Notes
Searing the Beef: Searing the beef before roasting helps lock in the flavors and gives the meat a beautiful brown crust.
Digital Thermometer: Using a digital thermometer is essential to ensure the tenderloin is cooked to your preferred level of doneness. The ideal internal temperature for a medium-rare tenderloin is around 130°F-135°F.
Resting Time: Allowing the cooked beef to rest for at least 10-15 minutes before slicing helps the juices redistribute, ensuring moist and flavorful meat.
Homemade Mushroom Gravy: Making gravy from scratch might seem daunting, but it goes really well with this dish.
Choosing Mushrooms: Use a variety of mushrooms for a deeper flavor. Porcini, cremini, or shiitake mushrooms would all work well.
Nutritional info is an estimate and provided as courtesy. Values may vary according to the ingredients and tools used. Please use your preferred nutritional calculator for more detailed info.