Combine the horseradish mustard and garlic paste together and slather onto the tenderloin.
Generously season the beef tenderloin with kosher salt and cracked black pepper to taste.
Place the tenderloin directly on the smoker and cook until the internal temperature reaches 125-130°F. Remove from the smoker.
Reverse Sear
Increase smoker temperature to the highest setting. Once temperature has risen, sear the tenderloin on all sides 2-3 minutes. Watch your internal temperature and remove before it gets to 140°F.
Remove from the smoker for the final time and allow to rest 10-15 minutes before serving.