I make mine as follows with Xmas day cooked and cooled leftovers comprising of:
sprouts with bacon and chestnuts
carrots
peas
roast potatoes
parsnips
red cabbage
pork stuffing balls
few pigs in blankets
roughly cut all into slices / chunks
dollop of Xmas gravy
fry a couple of leeks and an onion,
cook a couple of potatoes in microwave and , skin on and roughly mash with butter and add
add stuffing and pigs in blankets to the pan for a few minutes
add rest of veg and mix
season with a lot of salt and Pepper and big slice of butter and roughly mash with a fork plus a few mashed with potato masher
BUT don’t over mash!
add a bit of Garlic salt
grease a dish with butter, roughly put into it, don’t flatten or squash it
bake in oven 180 for 45-50 mins
turn out on a board - or keep in dish to serve
thus is my trial and error version I have honed over many years! Yum
if you don’t have everything- it’s cool, I just wing it usually - if no leeks - use onion etc