01 - 
                Melt 1 tablespoon butter in a large pot over medium-low heat. Add sliced onions with a pinch of salt, stirring frequently. Cook until deeply caramelized, approximately 30 to 40 minutes, ensuring they do not burn. Stir in chopped sage and transfer onions to a bowl.
              
              
              
                02 - 
                In the same pot, add remaining butter and return to medium heat. Add spinach, stirring occasionally until wilted. Add chopped garlic and cook for 30 seconds until aromatic. Remove from heat and set aside.
              
              
              
                03 - 
                Preheat oven to 230°C. Line a roasting pan or baking tray with aluminum foil and lightly grease. Place tenderloin on a cutting board and carefully slice lengthwise to butterfly, creating a flat surface. Season interior with salt and black pepper.
              
              
              
                04 - 
                Spread cranberry sauce evenly over the butterflied pork, leaving a border around the edges. Layer wilted spinach, caramelized onions, and sprinkle crumbled goat cheese over the top. Tightly roll up the tenderloin and secure with kitchen twine. Season exterior with salt and black pepper.
              
              
              
                05 - 
                Place the rolled pork onto the prepared pan. Roast in the preheated oven for 30 to 35 minutes, or until internal temperature reaches 60°C to 63°C.
              
              
              
                06 - 
                Remove from oven and let rest for 20 minutes before slicing. Serve with additional cranberry sauce, gravy, or preferred sides.