Remove the beef tenderloin roast from the fridge and let it sit at room temperature for 1 hour before roasting. Remove the silver skin and any excess fat from the tenderloin. Silver skin is a thin layer of fibrous connective tissue on the top of beef tenderloin. It is often removed by the butcher, but if not, you will need to do it yourself. It's easy to do, you just need to slip a sharp knife underneath the silver skin and slice close to the meat while pulling on the silver skin to remove it.

Next, tie up the whole beef tenderloin using kitchen string, starting at one end and making loops around your hand that you can slide over the tenderloin every inch or so. This will help the beef tenderloin cook more evenly, especially if one end is thicker than the other. Larger, whole beef tenderloin roasts have a thinner "tail" piece that can be folded over and tied up to make an evenly sized roast that will cook much better throughout.

Preheat oven to 450 degrees F. Pat the beef tenderloin dry with paper towels and season by sprinkling it with salt and pepper on all sides. Prepare the garlic herb butter by combining the butter, garlic, rosemary, thyme, oregano, salt, and pepper in a small bowl and mashing it with a fork. Divide the garlic herb butter in half, setting one part aside in a separate bowl for after the roast is done cooking.

Heat a large cast iron skillet or heavy pan over medium-high heat. Add the olive oil. When the oil is hot, place the whole beef tenderloin into the skillet and let it sear on 3 of the 4 sides for 2-3 minutes. We aren't trying to cook it through, just to develop a nice, flavorful crust to the tenderloin. Turn it over with tongs to the final untouched side, turn off the heat, and rub the beef tenderloin all over with half of the garlic herb butter mixture.

Transfer the beef tenderloin to the oven in the skillet it was seared in, or place it in a roasting pan first if you don't have an oven-safe skillet.

For medium doneness, cook for 25-35 minutes in the preheated oven (depending on the size of your roast), until an oven-safe meat thermometer inserted into the thickest part of the tenderloin registers between 135 and 140 degrees F. The temperature of the meat will continue to rise another 5 degrees after it is removed from the oven while it is resting before slicing.

While the meat cooks, combine and mix all of the ingredients for the horseradish sauce in a bowl and keep in the refrigerator until ready to serve.

Remove the beef tenderloin roast from the oven and slather with the reserved garlic herb butter mixture, then let the meat rest for 10 minutes before slicing.

Serve with horseradish sauce, if desired.