Melt the butter in a skillet over medium heat, then add the diced onion and celery. Sauté for about 3 minutes until they begin to soften and become fragrant. Add the fresh sage and diced apple, cooking for another 2 minutes to let the flavors meld together. Pour in the chicken stock and salt, bringing it to a simmer. Let this cook for 5 minutes so the vegetables fully soften and the liquid reduces slightly. Stir in the crumbled cornbread and cook, stirring occasionally, until most of the liquid is absorbed—this should take about 3-4 minutes. The mixture should be moist but not soggy. Remove from heat, fold in the dried cranberries, and set aside to cool for 15 minutes. I like to use fresh sage here because it has a more vibrant flavor than dried, and the tartness from the cranberries really balances the richness of the pork beautifully.

While the stuffing cools, preheat your oven to 375°F (190°C). Remove the pork loin from the refrigerator to bring it to room temperature—this ensures more even cooking throughout. Place the pork on a cutting board and, using a sharp knife, carefully cut horizontally along the length of the loin, leaving about 1/4 inch of meat attached at the bottom so it opens like a book. Season the interior and exterior of the pork generously with salt and black pepper.

Spread the cooled cornbread stuffing from Step 1 evenly across the opened interior of the pork loin, leaving about 1/2 inch of space at the edges. Starting from one long side, tightly roll the pork to enclose the stuffing, then tie it securely with kitchen string at 2-inch intervals. Make sure the roll is tight enough that the stuffing won't escape during cooking. Place the stuffed pork on a baking sheet, seam-side down. Season the exterior with additional salt, pepper, and a light dusting of dried sage for extra flavor and aroma during roasting.

Place the baking sheet in the preheated 375°F oven and roast for 45 minutes, or until the internal temperature reaches 140°F when measured with a meat thermometer inserted into the thickest part of the meat (away from the stuffing). Remove the pork from the oven and transfer it to a cutting board. Let it rest for 10 minutes before removing the string and slicing—I always rest my pork because those 10 minutes allow the juices to redistribute, keeping every slice moist and tender instead of letting them run out onto the cutting board.