Preheat the oven to 400 degrees Fahrenheit. Add a layer of 3-4 cups sliced or shredded turkey to the bottom of a 9 x 13-inch baking dish. Make sure you have enough turkey to cover the bottom of the dish evenly. Drizzle over some chicken broth if your turkey is dry.
Spread a layer of 3-4 cups mashed potatoes evenly over the turkey.
Sprinkle 2 cups leftover vegetables over the potatoes.
Evenly pour 1 cup gravy over the top of the vegetables.
Add a layer of 3-4 cups stuffing to the top of the casserole. Drizzle with some chicken broth if your stuffing is on the dry side. Cover with foil and bake for 30 minutes. Remove the foil and bake for an additional 5-10 minutes, until the stuffing is golden and crisp.
Dollop the top of the casserole with cranberry sauce if desired and serve.
Notes
Make Ahead & Storage Instructions
Make Ahead: Instead of putting all of your leftovers into individual Tupperware, just layer them straight into a casserole dish, wrap tightly, and store in the fridge for up to 24 hours. When ready to bake, add an extra 5 minutes to the bake time to heat through.
Storage: Store leftovers in an airtight container in the fridge for up to 3 days. Reheat portions in the microwave in 30-second increments until hot.
Freeze: Wrap the assembled casserole tightly, and freeze for up to 3 months. Thaw in the fridge overnight and bake as directed.