Heat the butter and 2 tablespoons of olive oil in a large skillet over low heat. Add the shallots and rosemary sprigs, season with salt and pepper, and cook for about 1 hour, until the shallots are tender and caramelized. Remove and discard the rosemary and stir in the vinegar and sugar. Transfer the shallots to the bowl of a food processor and blend until slightly chunky.
Meanwhile, preheat the oven to 400°F. Drizzle the remaining 2 tablespoons of olive oil over the beef and season with salt and pepper. Place on a large rimmed baking sheet. Roast for 35 to 40 minutes, until a meat thermometer inserted into the thickest part of the meat registers 125°F. Remove from the oven and transfer the meat to a cutting board. Tent with aluminum foil and let rest for 20 minutes.
Slice the meat into ½-inch thick slices and arrange on a serving platter. Spoon the marmalade over the top and serve.