Preheat the oven to 375°F (190°C). In a small bowl, combine brown sugar, olive oil, garlic, salt, and pepper. Rub this mixture evenly over the entire pork tenderloin.

Place the seasoned pork in a large oven-safe skillet. Roast in the oven for 30-40 minutes, or about 20 minutes per pound, or until an instant-read thermometer inserted into the thickest part of the pork reads 145°F (63°C).

Remove the pork from the oven. Transfer to a platter and loosely cover with aluminum foil. Let the pork rest for 10 minutes before slicing.

In the same skillet used for the pork, melt the butter over medium heat. Add diced apple, cranberries, apple cider, brown sugar, apple cider vinegar, cinnamon, and nutmeg. Cook and stir occasionally for 12-15 minutes, or until the sauce thickens slightly.

Return the rested pork to the skillet. Spoon the cranberry apple sauce generously over the pork. Garnish with fresh parsley (optional). Slice and serve immediately.