I'm not an SW person - but saw this so have popped in to share what I know.
Peel the potato first. To get the hasselback cut, I do mine by putting two cutting boards either side of the potato and with a very sharp chopping night, make a series of paralell cuts. The potato isn't cut all the way through but has relatively close together cuts the whole length of it. I think it's best done with smallish potatos. The boards stop you cutting through. In classical cooking, I think the potato is cradled in a wooden spoon and then cut - but that seems more dangerous to me. Sprayed with oil, they get crispy quite fast in the oven. In the old days, I would have ladled with goose fat. However they work just as well with a spray on the tray, and a spray or two on top> My DH loves the new low fat version as much as the old style.
Enjoy.
Ali