01 - 
                Preheat oven to 375°F. Lightly grease a large casserole dish.
              
              
              
                02 - 
                Peel and cube sweet potatoes into ½-inch pieces. Peel and dice Gala apples to match sweet potato size. Dice onion finely.
              
              
              
                03 - 
                Melt butter in a large skillet over medium heat. Add onion and cook until translucent, about 3-4 minutes. Add sweet potatoes and cook for 6-8 minutes until edges soften but centers remain firm.
              
              
              
                04 - 
                Sprinkle flour over vegetable mixture and stir continuously for 1-2 minutes. Dissolve chicken bouillon powder in chicken broth, then gradually add broth while stirring continuously to prevent lumps.
              
              
              
                05 - 
                Bring mixture to a simmer. Stir in heavy cream, maple syrup, sage, thyme, salt, and pepper. Cook 3-4 minutes until sauce thickens.
              
              
              
                06 - 
                Fold diced apples into sauce, ensuring even coating to prevent browning and initiate tenderizing.
              
              
              
                07 - 
                Spread shredded turkey evenly in the prepared casserole dish. Pour sweet potato, apple, and sauce mixture on top, leveling gently with a spatula without compressing layers.
              
              
              
                08 - 
                Sprinkle Gruyère cheese evenly over the assembled casserole. Bake uncovered for 30 to 35 minutes until cheese is golden and bubbly and sweet potatoes are tender.
              
              
              
                09 - 
                Allow casserole to rest for at least 10 minutes to thicken sauce and stabilize slices before serving.