Prepare beef tenderloin by trimming (if it didn’t come trimmed). Set out tenderloin 1-2 hours before cooking so that it can come to room temperature.
Cut the tenderloin into two pieces, if needed, so that it will fit into a cast iron or oven-safe skillet. Tuck the long skinny end under itself to form a roast that is uniform in thickness. Tie with kitchen twine to secure.
Preheat oven to 450°F.
Coat tenderloin with coarse sea salt and cracked black peppercorns. The exact amount will vary, but sprinkle liberally and coat all sides of the tenderloin.
In a large skillet, heat canola oil over medium-high heat until oil begins to smoke. Place the tenderloin into the skillet and sear. Brown on each side for 3-4 minutes.
Spread 4 tablespoons of butter over the top and sides of the browned tenderloin. Add whole garlic cloves to the pan around the meat. Add a teaspoon of minced garlic to the top of the meat, if desired.
Place in the oven for 25-30 minutes or until the center of the meat registers 120-125°F (for medium rare meat).
Remove from the oven and tent with aluminum foil for 10 minutes (the juices will redistribute and the temperature should continue to rise to about 130-135°F.
Heat the remaining 1⁄4 cup of butter and minced garlic over medium heat until the butter begins to turn golden brown. Remove from heat and set aside.
Remove the twine from the tenderloin and slice into 3⁄4” sections. Drizzle with the garlic browned butter.
Garnish with a bit of freshly chopped parsley if desired. Serve immediately.