Herb and Garlic Sauce: Add all the ingredients together in a medium-size bowl until combined. Set it aside.
Beef: Coat the beef tenderloin on all sides with about a ¼ cup of the herb and garlic sauce. Also, season the beef on all sides with salt and pepper.
Next, add the 3 tablespoons of olive oil to a large sauté pan or rondeau pot over high heat until it begins to lightly smoke.
Place in the beef tenderloins, immediately turn the heat down to medium-high, add in the butter and cook for 2 to 2 ½ minutes on each side until very well browned.
Transfer the pan or pot to the oven and roast at 275° for 20 to 25 minutes or until it has reached a 120° to 125 internal temperature.
Remove the beef from the pan and let rest for 3 to 4 minutes.
Add on additional herb and garlic sauce, slice and serve. See notes about leftover sauce.
Notes
Make-Ahead: This beef tenderloin is meant to be served as soon as it is done resting. If you choose to make it ahead of time, the internal temperature may increase past your desire.How to Reheat: While I never recommend reheating a hunk of beef, I do realize you may not be able to eat it all. Slice the beef tenderloin into desired portions and add it to a large sauté or roasting pan or with about 1 cup of beef stock, covered in foil and cooked in the oven at 400° for 10 to 12 minutes.Reheating your steak will 100% cause it to increase in internal temperature most likely past medium and into medium-well.Storing and Freezing: Store this in a plastic container or covered in plastic and refrigerate for up to 4 days. It can also be frozen for up to 45 days covered in plastic. See note above for reheating.This is best prepared and served at a rare to medium-rare internal temperature to preserve as much flavor as possible.If you are unsure of the internal temperature, be safe and use a thermometer.You should try serving this with a side of sauteed mushrooms.If there is any of the herb and garlic sauce is leftover, it freezes well covered for up to 3 months.