You can't have Christmas dinner without some good roast veg. Potatoes are a must, and a little roast pumpkin and onion and garlic won't go astray either.

I also steam some green beans, just so there's something in the meal that isn't totally artery-clogging.
Let's start with potatoes. I par-boil them first (just peel and boil them in salty water for about 10 minutes). Then drain, and bash them around a bit in the pot with some salt, rosemary and a little semolina.
Now, there are two options.
1. When my turkey has been cooking for about an hour and a half, I pour off most of the juices from the dripping pan and save them for gravy and more basting. Then add the potatoes to the pan (with pumpkin if you like, but you don't have to parboil that), and let them roast while catching all that delicious turkey juice.
2. Pour a jar of duck-fat into the now-empty dripping tray, and let it heat up while the turkey does its last hour in the oven. When the turkey's out, crank the oven up as high as it will possibly go. When the fat is HOT HOT HOT, put in the potatoes. They'll need about 20 minutes each side. Duck fat has a higher burning point to other fats, so it can get REALLY hot. This will make them all crunchy and awesome on the outside, but it does mean resting your turkey for nearly an hour.
Either way, make sure your potatoes are the last thing you take out of the oven and serve at the table. They should be PIPING hot. Crunch crunch crunch.