One day before the cook, using the butcher twine, tie the beef tenderloin to make sure it is as uniform in shape as possible. Combine the thyme, rosemary, garlic, salt and pepper. Season the tenderloin liberally on all sides, including the edges, with the seasoning mixture. Wrap in plastic wrap and refrigerate overnight.
The next day, remove the tenderloin from the refrigerator and let the roast rest at room temperature for at least one hour.
Set the EGG for direct cooking without the convEGGtor at 550°F/288°C.
Add a Big Green Egg Cast Iron Skillet to the cooking grid; heat the oil and butter until it shimmers in the skillet. Carefully add the beef tenderloin roast, rotating often, until a golden-brown crust starts to develop on all sides, about 5 minutes total. Remove the cast iron skillet and the roast from the EGG.
Add the convEGGtor to set the EGG for indirect cooking at 300°F/149°C.
Place the beef tenderloin on the rib rack inside of the roasting pan and place the pan on the cooking grid. Connect the EGG Genius for 300°F EGG temperature and 125°F meat temperature. Roast the tenderloin until the internal temperature reaches your desired temperature; remember that the meat temperature will rise a few degrees while it rests. Disconnect the EGG Genius. Let the tenderloin rest for at least 15 minutes before slicing. Slice and serve with the horseradish cream sauce. Enjoy!
Horseradish Cream Sauce Instructions
For the horseradish cream sauce, mix all the ingredients together and refrigerate overnight.