Thanksgiving Shepherd's Pie with Stuffing Crust

About 2 1/2-3 cups of stuffing/dressing made from the recipe of your choice ((leftover is just fine))

About 1/2 cup turkey or chicken broth/stock

each medium Yukon Gold and Russet potatoes ((you can use all of one or the other, I'm just letting you know what I did).)

salt and pepper (, to taste)

about 2 ounces butter

about 1 cup warmed milk ((maybe a bit more. I just put it in a pan over medium heat until it was hot but not scalding))

fat ((you can use oil, butter, coconut oil, chicken fat--whatever you like here))

medium onion (, finely diced)

large rib celery (, finely diced)

large carrot (, finely diced)

poultry seasoning

salt and pepper (, to taste)

flour

chicken or turkey stock

sweet potatoes in 1/2" dice. ((I used about 1/2 cup or so, I guess))

diced chicken or turkey ((leftover is fine. If you're making "new," the meat doesn't have to be cooked all the way through since it'll bake up in the pie))

frozen peas

dried cranberries