Peel and portion potatoes evenly, just make sure you pick a size and stick to it. Cover with cold water and add the salt and baking soda. The baking soda creates extra fluffy surface that will be so crispy when roasted.

Bring potatoes to a boil and reduce heat and simmer for between 5 and 10 minutes. Do not allow the potatoes to cook fully, what you want is for the surface area to be fluffy when scraped with a knife but not soft in the centre, drain in a colander and leave to steam dry for a few minutes. Then transfer back into the pot.

Toss the potatoes around in the pan to rough up the edges, you can see in the 2nd image how fluffy the surface is. select a rimmed baking or roasting tray and add the duck fat or oil or lard.

Space out the potatoes on the tray or trays so that there is some gaps to allow the heat to crisp up all the surface, add a little oil to stop the fat burning then roast at 230c - 450f for about 20 minutes or until the bottom edges are super crispy. Turn them over and return to the oven for a further 10 - 15 minutes.

Serve on a plate or in a bowl for the family to dive into, I used the fork test for crispness and my god they were amazingly crunchy and fluffy in the centre. Best Roasties ever people. https://www.youtube.com/watch?v=1wIc8e-qb8U&t=33s