I always set my oven to 375°F first thing, since it needs a few minutes to fully heat up while I'm getting everything else ready. While it warms, I lightly grease my 9x13 baking dish with butter or a quick spray of cooking oil. This little step keeps the turkey layer from sticking to the bottom once it's baked.
I mix my shredded turkey with the cranberry sauce in a small bowl first, rather than adding them separately. This way, every bite of turkey gets a touch of that sweet-tart flavor instead of the cranberry sauce pooling in one corner. I spread this mixture evenly across the bottom of my dish as the very first layer.
Next, I spoon my mashed potatoes right on top of the turkey layer and gently spread them out with a spatula, being careful not to mix the layers together. I sprinkle my drained corn evenly over the potatoes so every scoop of casserole gets a little pop of sweetness and texture.
In the same bowl I used earlier, I whisk together my gravy and milk until it's smooth and pourable. I slowly drizzle this over the corn and potato layer, making sure to cover the edges of the dish too, since those spots tend to dry out fastest in the oven.
I finish by scattering my prepared stuffing loosely over the top, followed by a generous handful of freshly shredded cheddar cheese. I don't press the stuffing down because I want it to stay a little crisp and golden once it bakes rather than turning soggy.
I cover the dish loosely with foil and bake it for about 20 minutes, then uncover it for the last 10 to 15 minutes so the cheese and stuffing can brown nicely on top. I know it's ready when the edges are bubbling and the cheese has fully melted into a golden crust.