After you’ve par-boiled them, drain them and put them back into the empty pan with the lid on. Take outside (helps if it’s cold!) and lift the lid for a couple of seconds so that steam escapes. This makes the outside of the spuds go fluffy, and it’ll crisp up nicely in the oven.

You can also put some around the meat (if you’re roasting some) and let them absorb the delicious grease.

(Also you’ll need more than that)