Any of the vegetables listed above can be prepared and roasted in a good 1cm depth of rendered goose fat. (truth be told, good-quality lard, beef dripping or best olive oil can also be used to delicious effect.) The fat or oil should be thoroughly heated in a roasting tin in a fairly hot oven (200c/fan 180c/gas 6) before any of the vegetables go in.
They do not all take the same time to cook, so can be added at staggered intervals. Roasting times are as follows: potatoes 40-45 minutes; parsnips, celeriac, jerusalem artichoke, beetroot and swede 30-35 minutes; pumpkin, squashes, carrots, shallots and garlic 30 minutes; leeks 20 minutes.
All should be turned once or twice during cooking and seasoned towards the end with salt and pepper.