Butterfly the pork tenderloin and place it in a large bowl. Drizzle with oil and season with salt and pepper to taste. Set aside.
Combine orange juice, mustard, brown sugar, and rosemary. Set aside.
Heat a large 12" nonstick skillet over medium-high heat. Add pork tenderloin to the hot skillet. Cook for 5-6 minutes on the first side or until well browned. Flip and cook on the 2nd side for 5 more minutes or until just cooked through. Remove the tenderloin from the pan and place it on a rimmed cutting board and lightly cover it with foil to keep it warm.
Add orange juice mixture to skillet. Add any accumulated meat juices from the cutting board. Add dried cranberries and cook stirring until reduced by half (2-3 minutes). Be sure to scrape up any browned bits from the bottom of the skillet. Remove from heat and whisk in butter just until it melts.
Thinly slice the meat and place it on a serving platter. Spoon cranberry orange sauce on top and garnish with additional fresh rosemary, if desired.
Butterflying pork tenderloin allows it to cook quickly and evenly! To butterfly, place tenderloin on a large sheet of plastic wrap on a cutting board. Cut a slit about 2/3 of the way through lengthwise down the middle of the pork tenderloin. Open the tenderloin like a book. Cover with a second sheet of plastic wrap and pound it out with a meat mallet or rolling pin to an even thickness.