Prep the fillingHeat 1 tablespoon butter and 1 tablespoon olive oil in a large skillet over medium heat. Add diced onion and cook for 3-4 minutes until softened. Add apples, garlic, and sage, cooking for another 3-4 minutes until apples are just tender. Stir in breadcrumbs, cranberries, walnuts, salt, and pepper. Remove from heat and let cool completely.

Butterfly the tenderloinPlace pork tenderloin on a cutting board. Using a sharp knife, cut horizontally through the middle of the tenderloin, stopping about 1 inch from the opposite edge so it opens like a book. Cover with plastic wrap and gently pound to an even 1/2-inch thickness.

Season and stuffSeason the inside of the pork with salt and pepper. Spread the cooled apple mixture evenly over the surface, leaving a 1-inch border on all sides. Starting from one long side, tightly roll the pork up and secure with kitchen twine at 2-inch intervals.

Season the outsideMix together salt, pepper, garlic powder, and paprika in a small bowl. Rub the entire outside of the rolled tenderloin with the remaining olive oil, then season generously with the spice mixture.

Sear and roastPreheat oven to 425°F. Heat remaining butter in an oven-safe skillet over medium-high heat. Sear the stuffed tenderloin on all sides until golden brown, about 6-8 minutes total. Transfer skillet to oven and roast for 12-15 minutes until internal temperature reaches 145°F.

Rest and sliceRemove from oven and let rest for 10 minutes before removing twine and slicing into 1-inch thick rounds. Serve immediately, showing off those beautiful spiral slices.