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hard boil, salted water with baking soda, 1 to 2 minutes only

potato chunks + boiling water + baking soda + salt, boiled just long enough for the outermost layer to give. The soda makes the water alkaline, which breaks down pectin at the surface and frees a slurry of starch that clings to the outside of each piece — that slurry is what the crust is made of. Ordinary boiling water gives you a smooth surface with nothing to crisp. Stop at two minutes: taken to fork-tender the pieces are too fragile to move into hot oil without breaking, and broken potatoes shed starch into the fat and burn it