Place roast in a large resealable plastic bag and set into a shallow dish. Pour Soy Sauce over the roast and close bag. Marinate in the refrigerate at least 8 hours or overnight; turning roast occasionally to distribute marinade.
On the morning of the day you want to served this roast: In a large heavy frying pan or cast-iron frying pan, melt butter and Worcestershire Sauce together. Add the roast (and remaining soy sauce) and brown on all sides. NOTE: This step gives color and flavor to the meat. Remove from heat and set aside.
About 45 minutes before serving time, preheat oven to 450 degrees F.
Rare - 120 degrees F.
Medium Rare - 125 degrees F.
Remove from oven and transfer onto a cutting board; cover with a tent of aluminum foil and let stand 15 minutes before carving (internal temperature will rise 5 to 10 degrees after it is removed from the oven).
While the roast is resting, make a sauce out of equal amounts of sour cream and horseradish. This can be made 1 day ahead of time. Refrigerate until ready to serve.
NOTE: I also make Knorr Bearnaise Sauce (according to direction on the package). Add 1 teaspoon dried tarragon and fresh-squeezed lemon juice from 1/2 of a fresh lemon. This can also be made 1 day ahead of time. Refrigerate until ready to serve.
To Serve: Cut the roast into approximately 1/2-inch slices (can slice thinner if desired). Transfer onto a serving platter and serve immediately with the Sour Cream/Horseradish Sauce and/or Bearnaise Sauce.
Beef Tenderloin Roast Recipe: https://whatscookingamerica.net/karencalanchini/beeffiletmignonroast.htm