Boiling your potatoes with salt or vinegar before you roast them can help make your roasted potatoes come out crispier, but there’s an even better way. All it takes is a little baking soda.
According to J. Kenji López-Alt at Serious Eats, you should use Yukon gold potatoes, not russets or reds. They’re the perfect firmness or roasting. Slice them up into chunks, then get ready to rough them up with some boiling, alkaline water. Add half a teaspoon of baking soda to about two quarts of water and bring it to a boil. Add the potatoes, then reduce it to a simmer and cook for about five minutes.
When they’re done, the potatoes will be tender and the alkaline water will have broken down the pectin of the exterior of the potatoes so they’re covered in a starchy, potato slurry. That slurry will crisp up nicely when you roast the potatoes in the oven.
Parboiling your potato slices before roasting helps cook them evenly, and helps them crisp up quickly.
Simmering starchy baking potatoes in water (seasoned with salt) gelatinizes a layer of starch on their exterior surfaces. This layer will then dehydrate and brown as the potato roasts, creating a thick, crisp shell.
Once the potatoes are tender, remove them from the water. Then dress as you normally would with oil and spices and pop them in the oven. You don’t want to overboil the potatoes though, so he suggests you add a tablespoon of white vinegar to the water to stop the potatoes from falling apart.
This tip isn’t just useful for roasted potato slices either: You can apply this method to home fries, smashed potatoes, steak fries, or just about any other baked potato dish.