Roasted Beef Tenderloin with French Onion Au Jus

While the beef rests, melt the butter in the same skillet over medium-high heat. Add the sliced onions, thyme, and garlic. Cook, stirring occasionally, until the onions are caramelized, about 15 minutes.
Add the brown sugar and Worcestershire sauce, stirring to combine, and simmer until reduced by half.
Add the beef broth, and bring to a simmer. Season with salt and pepper to taste. Let it cook for another 10 minutes.
Serve:

Slice the rested beef tenderloin and serve with the French onion au jus.
Notes:
You can prepare the beef tenderloin ahead by seasoning it and storing it in the fridge. Bring it to room temperature before roasting