The secret is to cook them twice.
When you think about making fries in the oven, you'd be forgiven if the first word that comes to mind is not "delicious." Oven fries are a great way to satisfy a sudden urge for potatoes without much effort, but it's hard to get them to be like restaurant fries, particularly if you're putting them directly from the freezer bag into to the oven. They get cooked, yes, but the final product is often mushier than I'd like. What I'm always hoping for in a fry—and rarely get with the oven—is an extremely cripsy exterior and an interior that's soft and cooked through. In many attempts at oven fries, my potatoes will get crisp on the outside but not quite done in the center, or be mushy all the way through.
But then I remembered how you get hash browns or roasted potatoes to get that beautiful crispy, golden exterior, and realized my mistake all along. I had only been cooking my oven fries only once. If you want potatoes to be crispy without under-cooking the inside, the secret is to cook them twice. This goes if you're making them in the fryer or in the oven, but at home, it's way easier to turn on the oven than mess around wit hot oil, unless you're lucky enough to own a deep fryer.
So I used the trick to make potatoes with some leftover duck fat. You cut the potatoes into fries, par-boil them in water until they're still firm but definitely cooked, dry them off, toss in whatever fat you want (olive oil works just fine as would any other neutral oil), salt them, and then put them in the oven. It's basically the same method for these very excellent Smitten Kitchen oven fries. The pre-cooking ensures that the inside of your fries are done all the way through before they even get to the oven, so the time in there is only for developing that shatteringly crispy exterior. They're restaurant-quality fries, using just your humble home oven.