Prepare: Preheat oven to 375 F. Pat pork tenderloin dry with paper towels. If unseasoned, season all sides with salt and pepper.
Sear & Roast: Heat oven-safe pan over medium-high heat. Coat bottom of pan with olive oil. Add pork and cook until browned on one side, about 4 minutes. Flip pork in pan, and transfer to oven. Bake at 375 F until pork is browned and cooked through, about 25 minutes (thermometer inserted in center should read at least 145 F; Note 5). Transfer pork to plate to rest; do not slice yet.
Make Sauce: Add all sauce ingredients to now-empty pan over medium heat. Use sturdy wooden utensil to loosen any browned bits stuck to pan. Stir until cheese and butter are melted. Let sauce simmer until thickened, about 5 minutes.
Serve: Slice pork into thin slices and drizzle sauce on top. Serve (Note 6).
