01 -
Preheat oven to 375°F and lightly grease a large casserole dish.
02 -
Peel and cube sweet potatoes into ½-inch chunks. Peel and dice Gala apples into similarly sized pieces. Dice the onion finely.
03 -
Melt butter in a large skillet over medium heat. Add diced onions and cook 3–4 minutes until translucent. Add sweet potato cubes and sauté for 6–8 minutes until edges soften but centers remain firm.
04 -
Sprinkle flour over the mixture and stir briskly for 1–2 minutes. Dissolve chicken bouillon in chicken broth, then gradually add broth to skillet, stirring constantly to avoid lumps. Bring to a simmer, then add heavy cream, maple syrup, sage, thyme, salt, and pepper. Cook 3–4 minutes until sauce thickens.
05 -
Add diced apples to the sauce and stir to coat evenly, preventing browning and beginning tenderizing process.
06 -
Evenly spread shredded turkey in prepared casserole dish. Pour sweet potato, apple, and sauce mixture over turkey, leveling surface gently without mashing.
07 -
Sprinkle shredded Gruyère cheese evenly over the top. Bake uncovered for 30–35 minutes until cheese is golden and bubbling, and sweet potatoes are fork-tender. Tent loosely with foil if cheese browns too quickly in final 10 minutes.
08 -
Allow casserole to rest for at least 10 minutes to thicken sauce and facilitate cleaner slicing.