Peel the potatoes and cut them into 1.5-inch chunks. Line a large roasting tray with baking paper and add the oil to the center. Place in the middle of the oven and set the oven to heat at 400ºF (200ºC)
Add potatoes to a large pot with enough water to cover the potatoes by about half an inch. Add one tablespoon of salt to the water, cover, and bring to a roiling boil. When fully boiling, uncover and cook for two minutes. Drain in a colander.
Quickly dry the pot if needed with some paper towels and add the potatoes back to the pot. Cover the pot with a lid and shake energetically up and down and back and forth until the outside of the potatoes has been roughed up.
Remove the roasting pan from the oven and gently tip the potatoes into the middle of the pan (be careful not to get splattered with hot oil). Using two tablespoons, toss the potatoes in the hot oil until coated with oil, and space the potatoes at least half an inch apart. Return to the oven for 15 minutes.
Remove the pan and flip the potatoes using the two spoons again, so that the side that was touching the bottom before is now facing upwards. Roast another fifteen minutes.
Remove the pan and use a slotted spoon, fish slice, or slotted spatula to remove the potatoes from the oil and add them back to the pot you were previously using. Return the roasting pan to the oven to keep the oil hot.
Add the harissa paste to the pot and gently toss the potatoes using the two spoons until they are fully coated. Sprinkle over the remaining teaspoon of salt and toss again. Retrieve the pan from the oven, gently toss the potatoes in the oil, and roast for five minutes.
Flip the potatoes and roast for five minutes more.
Done. Check the potatoes are cooked through and adjust seasoning if needed.