Preheat oven to 450°. Combine garlic, rosemary, lemon peel, salt, and pepper. Press mix into tenderloin. In large skillet with oven proof handle, heat oil over medium heat. Add tenderloin and cook, turning until brown, 8-10 minutes. Transfer to oven. Roast 10 minutes. Remove pork from pan and keep warm.

Set skillet over high heat and stir in broth and vinegar, scraping up browned meat. Bring to boil and cook until reduced by 1/2. Whisk in 1 tablespoon of butter at a time. Stir in capers (optional). Cut into thick slices and serve with sauce.