Christmas Dinner: Part 3, Roast Potatoes and Mash

Double carbohydrates are good. I don't care what y'all healthy-eaterists have to yak about it.
If you don't want to do potatoes both ways, you don't have to, but obviously the roasts are a bit of a must for a roast dinner.
I read up on all sorts of revolutionary ways to roast potatoes, but for me, this one, the way my whole family make it, is simple and very effective.
1)Boil some chunked, peeled spuds (boil them by having them in cold water, and bringing them up to boiling) until you can get a knife through it, but they shouldn't be soft. About 10 minutes.
2)In the meantime, put a few tablespoons of goose fat (or vegetable oil if you can't find goose fat, but it really does add goldenness and extra flavour) in a roasting tin and let it melt in the hot oven.
3)Drain the potatoes, return half to the pan and give the other half a brief shake, so the edges just start crumbling. This gives extra surface area for the salt and fat to cling to. Salt and fat. Salt and fat! SALT AND FAT! YOU WILL DIE MWUHAHAHAHAHA
4)Tumble the spuds into the goose fat, season generously with salt and pepper and dried thyme. I felt thyme was a loved herb that's been a little underused this Christmas so I included it here. Any Provencal herb like rosemary would do just fine. Spoon the goose fat over and roast until golden and crisp, about 45 minutes.
5)With the remaining potatoes, boil them for about another 10 minutes until very soft, then give them a good mash with some milk, pepper, salt and a fat such as olive oil, but you know you want butter. Salt and fat. Salt and- no just joking. Mash well, whilst also giving it a good fold and lift the potatoes up and down a lot to whip some air into them. Put them in a serving dish and a lovely touch then is to perk it up in peaks with a fork, purely for aesthetic value. It's obviously not essential and not very wise either as it makes it go cold faster, but doing this makes it look so Christmassy somehow.