Remove the beef tenderloin from the refrigerator and let it come to room temperature (about 1-2 hours depending on the temp of your fridge.)
Preheat the oven to 450 degrees Fahrenheit.
Toss the veggies in olive oil, salt and pepper.
Evenly place the seasoned cauliflower, turnips, garlic and shallots into a roasting pan. Place the rack on top.
Spread the seasoned carrot slices evenly on a separate sheet pan.
Once the tenderloin has come to room temperature, brush it with olive oil. Coat evenly in salt, pepper and garlic.
Heat a skillet on medium high heat. Season it with 1 tbsp olive oil until the oil is hot, and the pan is fully coated. (You want a thin shimmering layer of oil, not a lot.)
Place the tenderloin on the skillet and sear for 3 minutes per side, until each side is browned.
After all sides of the tenderloin are thoroughly browned, place it on a roasting rack above the cauliflower and turnips.
Keep the tenderloin juices in the skillet, and blot to get rid of any large clumps. Add butter, rosemary, salt and pepper. If the butter is salted, you can just add rosemary and pepper.
Pour all of the rosemary butter onto the tenderloin, while it's on the rack pan over the bed of vegetables. (You can also wait to do this at the end, but I like to let it cook with the butter on top, so the veggies soak up the flavor.)
Roast the tenderloin for 25 minutes. The internal temperature should be about 127 when you take it out of the oven because it will continue to cook while it rests.
Let the tenderloin rest for 10 minutes. Check the internal temp to make sure it's around 135. It should be 130-135 internally before serving. If the temperature does not reach 135, put it back in the oven for 5 minute increments until the temperature is high enough for your comfort level. 140-145 F is medium, but I highly recommend this cut of beef on the rarest medium rare side :D Mine had an internal temp of 135 exactly.
Slice it into 1-inch thick medallions.
Plate the vegetables on the bottom of a large platter. Top the vegetables with the tenderloin slices. Pour any excess jus on top of the steak, or throw it in a pan with butter, garlic, shallots, and a hint of red wine for a nice pan sauce. I skipped the pan sauce it was divine.