1. One of the reasons that Nigella's recipe works is because the smoke point of duck and goose fat is so high. Coating the potatoes in the hot oil when they go into the oven helps immensely in creating a crunchy crust. The hotter the oil, the better the crust.
The oils I have listed have high smoke points i.e. they can be heated to a high temperature in the oven without smoking.
2. Perfect roast potatoes start with the right potato. It has to be a potato with a high starch content so it will bake with a fluffy inside and will soak up the oil to form a crusty exterior.
Australia - the common dirt brushed potatoes (Sebago) work great with this, it's a great all rounder. Otherwise, any of these are great all rounder potatoes for this: Desiree, Golden Delight, Kennebec, King Edwards, Pontiac, Red Rascal, Royal Blue, Spunta.
US - russet is ideal. Yukon Gold is not suitable.
UK - Maris Piper is a good all rounder which is suitable and readily available in all the supermarkets. King Edwards and Desiree are also great.
3. This might seem like alot of salt but you lose some of it in the roughing up.
4. Size matters. If the potato is too small, they will overcook before the outside becomes crunchy.
5. The roasting time depends on the strength of your oven, oil, how much you preheated the oil, and how heavy based the roasting pan is.
6. These potatoes do not roast to a dark golden brown that you may be used to with ordinary roast potatoes. They will be crunchy when they are a golden brown colour with only some browned edges.
7. Nigella's recipe has the same steps except she uses goose fat instead of normal oil. Her recipe calls for 1lb 5oz / 640g of goose fat which is 2 cans. Also she uses 5lb/2.5kg of potatoes which doesn't fit into any of my pans so I reduced the amount of potatoes.