Preheat the oven to 250 degrees.
Prepare the roast by placing it onto a plate then slice a large clove of garlic into several thin spears.
Use a sharp knife, pierce meat on both sides about 1/2-inch deep and insert slivers of garlic in each hole, pushing all the way in.
Drizzle some olive oil evenly on both sides of the roast, then rub it in. Season the entire roast very well with sea salt and freshly cracked pepper, to taste.
Coat a cast iron skillet or Dutch oven with cooking spray and heat over medium high heat.
Once the pan is HOT add the roast and sear on all sides.
Place the meat thermometer into the thickest part of the roast.
Place the cast iron skillet into the preheated oven and cook until the thermometer reads 115 degrees, about 45-60 minutes.
Crank the heat up to 500 degrees and continue cooking until the roast reaches 125-130 degrees, for medium rare.
Remove from the oven and let the roast rest on a cutting board for at least 10 minutes before slicing and serving. Enjoy.
Make the creamy horseradish sauce while the beef is roasting, by combining the sour cream, mayonnaise, cream of horseradish, lemon juice, Worcestershire sauce, and sea salt & freshly cracked pepper, to taste. Mix until well combined. Taste and add any seasonings you think it needs. Set aside in the refrigerator for flavors to mingle.
Once the meat has rested. Slice and serve with the sauce. Enjoy!