Boiling potatoes then roughing them up before roasting
adds surface area and extra crunch.Our secondary goal is to increase their surface area.
Craggy, uneven surfaces crisp up a lot better than smooth
ones. Luckily, we can kill two birds with one stone here.
By boiling your potatoes before you roast them, not only
do you ensure that their outer layers of starch are
properly gelatinized, you also soften their exteriors
enough that they get a bit battered and bruised when you
toss them around with oil before roasting them. This
creates a sort of potato-oil paste that adds plenty of
surface area and acts almost like a batter for fried foods,
creating an extra layer of crispness as the potatoes roast.
Take a look at these potatoes, roasted side by side in
the same oven. One batch was started raw, another was
boiled first, and the third was boiled, then roughed. The
difference is obvious.