There are three crucial things that I think make the difference here: the first is the heat of the fat – if it’s not searingly hot, you don’t stand a chance, and since goose fat has a very high smoking point and tastes good, it is my annual choice. The second is the size of your potatoes – you want them relatively small, so that the ratio of crunchy outside to fluffy interior is optimised. Finally, dredging the potatoes – and this is a family practice, inherited through the maternal line – in semolina rather than flour after parboiling, then rattling the pan around to make the potatoes a bit mashed on the surface so they catch more in the hot fat, is a major aid. The roast potatoes become vegan if you roast them in solid vegetable fat or oil.