For the crispiest fried or roasted potatoes, dip them in ice water first.
“It’s a well-known trick to soak fries in ice water to make them crispy, but standard practice is to soak them for a few hours. Whenever I’m cutting potatoes for frying or roasting in oil, I throw them in a bowl of ice water as I go. When I’m done, I swirl them to wash off excess starch, then drain, then pat dry. They don’t soak for more than a few minutes, but even this short period is long enough to make them really crispy and significantly reduce how much they stick.” —cellists_wet_dream