Step 1: Prepare the Beef Tenderloin

1. Season the Beef: Preheat your oven to 275°F (135°C). Rub the beef tenderloin generously with olive oil, salt, and black pepper, ensuring it’s evenly coated.
2. Add Fresh Herbs: Place rosemary and thyme sprigs around the tenderloin, gently pressing them onto the surface. This infuses the beef with a delicate, herby aroma.
3. Arrange Shallots: Place the halved shallots around the tenderloin in the roasting pan. These will caramelize and add a lovely sweetness to the dish.

Step 2: Slow Roast the Beef

1. Roast the Tenderloin: Place the roasting pan with the beef and shallots in the oven. Roast for 1 hour to 1 hour 15 minutes, or until the internal temperature reaches 130°F (54°C) for medium-rare.
2. Rest the Meat: Remove the tenderloin from the oven, tent it loosely with foil, and let it rest for at least 15 minutes. This step allows the juices to redistribute within the meat, resulting in a more tender and flavorful bite.

Step 3: Prepare the Port Wine Reduction

1. Reduce the Port: In a small saucepan, combine port wine, beef stock, and balsamic vinegar. Bring to a boil, then reduce the heat to low and let it simmer until the liquid reduces by half and becomes syrupy. This usually takes about 15-20 minutes.
2. Finish the Sauce: Stir in the butter until melted and smooth, which adds richness and sheen to the sauce. Season with salt and pepper to taste.

Step 4: Serve

1. Slice the Beef: Slice the beef tenderloin into thick slices. Arrange on a platter with the caramelized shallots.
2. Drizzle with Port Reduction: Pour the port wine reduction over the beef slices and shallots, or serve on the side for guests to drizzle as desired.
3. Garnish: Garnish with fresh rosemary or thyme sprigs for an elegant presentation.