Preheat the oven to 200C/400F. Add 3-4 tablespoons of vegetable oil to the base of a large, sturdy baking tray and move the tray around to ensure the entire base is coated. Set aside.
Bring a large pot of well salted water to the boil. Use your largest to ensure there is some wiggle room – the baking soda will bubble up a little when you add it.
Once the water is boiling, add the baking soda. When the bubbles subside, add the potatoes. Boil until the potatoes are about 90% cooked through. A knife should slide through the potato with just a little bit of resistance. This depends on the potato size but could take 10-20 minutes.
Retrieve the potatoes from the water and allow to dry off for a few minutes.
Place your tray with oil into the oven to preheat for five minutes.
Cut the potatoes into your preferred size, but not smaller than a 50c coin. Really small pieces of potato tend to break up in the next stage, so err on the side of caution. I keep the skin on my potatoes and I recommend you do too.
Mix the 3 tablespoons of oil, parmesan, pepper and 1/2 teaspoon salt in a large bowl. This bowl will need a ‘lid’ so make sure you have a plate or a tray large enough to cover the mouth of the bowl. You could also do this in a medium/large container if you’d prefer.
Add the potatoes and give them 3-5 vigorous shakes, then assess. A mash potato like starchy slurry should have formed or be forming on the surface, grabbing the parmesan. If not, continue to shake until it does. You don’t want the potatoes to break up into mash, but you do want a decent amount of parmesan slurry on each potato. This is what will go so crispy in the oven.
Once you’re happy with the look of the potatoes, very carefully take the tray out of hot oil out of the oven. I open my oven door from the side to ensure I don’t get hot oil eye burn. Nothin’ worse.
Working quickly, use tongs to add the potatoes to the hot oil. They should sizzle significantly on impact. Spread them out, then pop them quickly back into the oven. Bake for 15-20 minutes, then use tongs to flip the potatoes over. The bottoms should be golden brown. If you try to move a spud and the parmesan breaks off, just pop it on top of the potato. Move any crispy parmesan bits to a potato top, as they will adhere on baking. Cook for another 15-20 minutes or until the parmesan and potato are crispy and delicious. Remove the potatoes from the tray and give them a final sprinkle of salt while they’re hot, as the salt will cling to the oil.
Serve hot, but the leftovers are significantly less leathery than other crispy potatoes.